transcription-vert

unit1ripe n.成熟rip v.裂口rupt-词根：破interrupt v.打搅，打断corrupt v.贿赂a.腐败的corruption n.腐败; 贪污; 贿赂;erupt v.（火山）爆发disrupt v.崩溃；瓦解rupture n.破裂claim-词根：喊叫proclaim v.宣城scream v.尖叫exclaim v.呼喊reclaim v.要求归还acclaim v.欢呼；喝彩claim v.要求；声称verse-vert-词根：旋转invert v.倒置,倒转,颠倒avert v.躲避；转移convert v.皈依；兑换；变换divert v.转向diversion n.转向verse-词根：旋转reverse n.相反;背面a.相反的v.颠倒,倒转adverse a.不利的，有害的conversely ad.相反地conversation n.会话,谈话verse n.诗节prose n.散文universe n.宇宙universal a.普遍的;宇宙的university n.(综合)大学controversial a.引起争议的controversy n.争议diverse a.多种多样的,(from)不同的diversion n.转向,转移;牵制;解闷;娱乐divorce v./n.离婚,分离version n.版本;译本,译文;说法edition n.版本（编辑的）versatile a.多才多艺的；多功能versus prep.对抗inverse a.相反的quiver v.颤抖sist-站subsistence n.维持生计insist vi.(on)坚持要求exist v.存在;existence n.存在resist v.抵制resistant a.抵制的resistance n.抵制transistor n.晶体管consist v.(in)存在于;(of)由…组成,由…构成consistent a.(in)前后一致的；（with）一致，符合persist v.持久persistent a.持久的stand v.站assist vt.协助assistant n.助理assistance n.协助dict-说contradict v.反驳contradiction n.反驳predict v.预测diction n.语言dictionary n.字典dictate v.命令dictator n.独裁者indicate v.暗示；表明indication n.暗示；表明indicator n.指数indicative a.表明的addict n.上瘾的人a.上瘾的addiction n.上瘾verdict v.裁定very a.非常的；真正的doc-词根：写下来document n.文件documentary a.文件袋n.纪录片orthodox n.正统的，东正教的paradox n.悖论；矛盾pose-放propose v.建议；求婚proposal n.建议；求婚proposition n.建议suppose v.假设supposal n.假设deposit v.沉淀；存款impose v.强迫；征税expose v.暴露exposure n.暴露compose v.组成；作文；作曲composite a.组成的composition n.组成；作文；作曲composure n.镇静，沉着;pose n.姿势v.摆放posture n.姿势put v.放dispose v.处理；处置disposal n.处理；处置disposable a.可降解的；一次性的positive a.确定的；积极的；肯定的pending a.不确定的penis n.阴茎position n.位置; 地位，职位;post n.邮局；岗位v.张贴opposition v.反对possess v.占有possession n.占有；占有物obsess v.着迷，萦绕obsession n.着迷，萦绕purpose n.目标preposition n.介词spect-看spy n.间谍v.偷inspect v.检查inspector n.检察员retrospect v./n.回顾；追溯[反]foresee perspective a.透视的n.透视图;观点introspect v.内省respect v.尊敬；尊重respectable a.可敬的respectful a.毕恭毕敬的irrespective a.不考虑的respective a.各自的prospect n.前景spectator n.观众spectacle n.奇观spectacular a.奇观的specimen n.样品speculate v.推测，投机calculate v.计算; 估计;aspect n.方面；外貌respect v.尊敬suspect v.怀疑suspicion n.怀疑suspicious a.怀疑的sceptical a.怀疑论的；怀疑主义的skeptical a.怀疑论的；怀疑主义的despite prep.尽管despise v.鄙视expect v.期盼expected a.期待的unexpected a.始料未及的conspicuous a.有目共睹的press-压pressure n.压力suppress v.镇压（运动）depress v.压抑（情感）depressed a.压抑的impress v.给…深刻印象（褒义词）impressive a.令人印象深刻的impression n.印象express v.表达n.特快专递expression n.表达expressive a.表达的repress v.抑制（情感）compress v.压缩compressed a.压缩的compression n.压缩pressure n.压力fact-fect-fict-词根：做factory n.工厂，制造厂factor n.因素facile a.容易做的（对付事儿的）facility n.容易facilitate v.使容易facilitator n.援助者fact v.事实exact a.确切的exactly ad.确切地unit2fect-f词根：做defect n.瑕疵；缺点infect v.感染；传染infection n.感染；传染infectious a.感染的；传染的effect n.效果；结果effective a.有效果的efficient a.效率高的;perfect adj.完美的;affect vt.影响(疾病)；感动affection n.疾病；感情suffice v.足够sufficient a.(for)足够的deficient a.不足的deficiency n.缺失deficit n.亏损art n.艺术；技术artificial a.造作的；人造的profit n.利润profitable a.有利可图的fer-词根：运输、携带prefer v.更喜欢preference n.更喜欢；偏好suffer v.遭受infer v.推论inferior a.次要的defer v.屈尊；耽搁deference n.屈尊；耽搁refer v.提及；参考refer to 指的是transfer vt./n.转移；转换；过户；改乘confer v.授予conference n.(正式)会议differ v.不同difference n.不同interfere v.(in)打搅；干扰;intervene v.干涉；干预interference n.(in)打搅；干扰;ferry v.摆渡fertile adj.肥沃的; 可繁殖的;fertilize v.施肥fertilizer n.肥料fertilization n.施肥offer v.提供n.机会metaphor n.隐喻ferrycarry v.运输tain-拿contain v.包含，容纳container n.容器content n.内容a.满意的take v.拿sustain vt.支撑sustainable a.可支撑的sustainability n.可持续的detain v.扣押；耽搁retain v.保留retention n.记忆力attain v.（经过努力）达到protein n.蛋白质vitamin n.维生素; 维他命;insulin n.胰岛素;pertain v.有关pertinent a.相关的entertain v.招待；娱乐entertainment n.娱乐maintain v.维持；持有观点maintenance n.维持obtain v.获得tennis n.网球scribe-写rub v.擦，摩擦rubber n.橡胶; 橡皮;catch v.抓scratch v.挠prescribe v.指示；规定；开处方prescription n.处方subscribe v.签署同意；订阅；认捐subscription n.订阅；认捐describe v.描述；描写description n.描述；描写inscribe v.题；刻transcribe v.誊写; 改编transcription n.誊写ascribe v.归…于script n.手稿tect-盖子detect v.发现detective a.发现的n.侦探detection n.发现protect v.(from)保护,保卫sect-切section n.部分insect n.昆虫intersection n.十字路口sector n.部门，部分；section n.部分; 节; vi.切开; segment n.段,片,节,部分segregate v.隔离execute v.执行;执行死刑executive a.执行的n.总经理execution n.执行plex-/plic-叠x-象形implicit a.含蓄的explicit a.坦率的complicate v.使复杂complicated a.错综复杂的perplex v.使困惑surplus a.过剩的,剩余的replicate v.折叠；复制duplicate v.折叠；复制ply-词根：叠supply v.(with,to)供给,供应, supplyer n.供应商imply v.暗示；含蓄implication n.意义；含义reply v.回答comply v.遵守；服从compliance n.遵守；服从compliment n./v.称赞,恭维apply v.申请；应用application n.申请；应用applicable adj.适当的; 可应用的;gress-词根：行走progress n/v.进步progressive a.进步的,先进的;前进的regress v.倒退；回归；退化regression n.衰退；回归；退化congress n.(代表)大会;(美国等国的)国会,议会congressional a.国会的; 议会的; aggressive a.侵略的，好斗的，有进取心的aggression n.上进心transgress v.越轨；违背（道德）digress v.偏题，miss-投、射promise v.承诺n.希望promising a.有希望的compromise v.妥协；损害submit v.递交；投降submission n.递交；投降transmission n.转播；传递；转发commission n.委员会;委任,emission n.发射（废气）dismiss v.解散；解雇；驳回missile n.导弹a.可投射的mission n.使命missionary n.传教士message n.信息messenger n.信使mit-投、射submit v.递交；投降transmit vt.转播；传送commit v.委托;犯(罪)committee n.委员会,全体委员emit vt.排放（废气）;发表;发行intermittent a.间歇的,断断续续的omit v.漏掉fess-说professor n.教授profession n.表白；宣布；文职professional a.职业的n.专业人员prophet n.预言家;prophecy n.预言; professor n.教授confess v.坦白; 忏悔fess v.坦白，供认unit3form-词根：形状、形成transformer n.变形者deform v.使变形（破坏）inform v.(of,about)通知informed a.消息灵通的information n.通知,报告;情报,资料,消息;信息reform v./n.改革,改造,改良transform vt.变形；变化;变压;conform vi.(to)遵守perform v.完成；表现;表演performer n.表演者performance n.表演,表现；性能uniform n.制服form n.形状,形式;表格v.组成,构成;形成formal a.正式的;形式的formula n.(pl.formulae)公式;规则;formulate v.用公式表达；清晰的表达voc-词根：声音voice n.声provoke v.挑动provocation n.挑衅；招惹；激怒provocative a.挑衅的；招惹的advocate vt.鼓吹，提倡n.提倡者naïve adj.幼稚的；天真的；单纯的;vocable n.词vocabulary n.词汇,词汇量;词汇表vocal a.声音的vocation n.召唤;天职;职业vow n.誓言; 郑重宣布;vt.& vi.起誓，发誓; 郑重宣告;vowel n.元音；母音;evoke vt.唤起(回忆、感情等)；引起vis-/vid-看visit v/n.访问,参观provide v.提供,准备,假设；规定provided conj.倘若,只要,假如provident adj.有远见的，节俭的;provision n.供应；条款;survey v./n.俯瞰;社会调查surveillance n.监控;invisible a.看不见的,无形的revise v.修订review v.复习preview v.预习visible a.看得见的vision n.视觉;远见;洞察力;visitor n.访问者；参观者visual a.视觉的oral a.口头的aural a.听觉的manual a.手工做的,体力的n.手册,指南physical a.物质的；身体的;物理的visa n.(护照等的)签证;维萨信用卡vt.签证evidence n.明显;显著;根据;证据;迹象evident a.明显的,明白的advice n.劝告，忠告，(医生等的)意见advise vt.忠告，劝告，建议；通知，告知envisage vt.正视; 想象;duce-词根：引导introduce v.介绍，引荐deduce v.演绎；推导，生产deduct v.扣除deductible a.可扣除的induce v.导致；引导reduce v.减少,reduction n.减少conduct n.行为v.操作conductor n.操作者；运行者semiconductor n.半导体educate v.教育,培养,训练education n.教育,培养,训练introduce v.介绍，引荐introduction n.介绍produce v.生产product n.产品production n.生产；总产量productive a.高产的reproduce v.繁殖;复制flu-词根：流flow v.流superfluous a.过剩的influence n.渗透力；影响力v.影响influential a.有影响的n.有影响的人affluent a.富足的；富裕的n.富人flu n.流感fluent adj.流畅的; 流利的;fluid adj.流体的n.液体，流体;fluctuate v.浮动；起伏ject-投、射project n.方案,项目v.投射,投影subject n.主题;主体，实验对象v.受制于subjective a.主观的inject v.注射eject v.弹出reject v.拒绝adjective n形容词pel-词根：推palm n.手掌propel vt.推进propeller n.螺旋桨，推进器;impel v.推进expel vt.驱逐;repel vt.击退;compel v.强迫compulsory a.必须做的necessary a.必须的spir-词根：呼吸spirit n.精神inspire vt.鼓舞inspiration n.灵感respire v.呼吸conspire v.串通一气，合谋conspiracy n.密谋perspire v.排行aspire v.渴望；立志得到aspiration n.志向，抱负;volve-词根：旋转involve v.卷入,牵涉;包含evolve v.(使)发展;(使)进化evolution n.发展,进化revolt v.革命；反叛revolution n.革命;反叛revolutionary a.革命的,革新的n.革命者revolve v.(使)旋转;思考envelope n.信封stit-词根：站stand v.站substitute v.(for)代替n.代替品institute v.建立n.学院institution n.机构institutional a.机构的；制度的constitute vt.组成，任命；制定法律constitution n.宪法constitutional n.宪法的constituent a.组成的；选民curs-/cur-词根：跑course n.过程；v.快跑current n.气流；水流；电流currently ad.当前的currency n.货币occur v.发生concur v.同时发生recur v.再次发生（贬义词）incur v.招惹precursor n.先驱excursion n.远足；郊游course n.过程v.快跑cede-/ceed-走precede v.领先precedent n.先例unprecedented a.史无前例的preceding a.领先的proceed v.继续proceeding a.继续的procedure n.程序succeed vi.成功；继承vt.接替；继…之后exceed v.超出concede v.让步；认输recede v.渐退unit4cess-词根：走process n.过程,工序v.处理procession n.处理success n.成功successful a.成功的succession n.继承successive a.继承的successor n.继承者excess n.超出a.超出的excessive a.超出的predecessor n.前任recession n.衰退access n.入口v.接近accessory n.附件；同谋accessible a.可达到的concession n.让步；认输；迁就sent-词根：感觉sense n.感觉；理性essence n.本质,进化essential a.本质的,必须的esthetic adj.感觉上的; 美学的; 审美的; aesthetic a.(esthetic)美学的，美的artistic adj.艺术的; 有美感的; 风雅的resent vt.反感；厌恶;consent v.同感consensus n. 舆论; 一致同意sensible a.明智的sensitive a.感性的；敏感的sentiment n.情绪sentimental adj.伤感的; 多愁善感的; scent n/v.香味，气味; 嗅觉;sess-词根：坐sit v.坐assess vt.评估；征税；评价session n.(一届)会议,一段时间vac-空cave n.洞evacuate vt.撤离，疏散; 排泄;vacuum n.真空; 空白;vacant adj.空闲的；空缺的vacation n.休假,假期ceive-拿receive v.收到susceptible adj.易受影响的; 易受感染的; deceive v.欺骗,蒙蔽deceit n.欺骗，欺诈;receive v.收到reception n.接待conceive v.怀孕; 构思;concept n.概念，想法conception n.概念的形成perceive v.洞察；觉察；感知perception n.洞察；觉察；感知;cip-词根：拿receive v.收到recipient n.接受者a.收到的receipt n.收据，发票；收入;reciprocal a.互利的；互惠的mutual adj.共有的; 相互的(情感上的) disciple n.信徒；门徒；追随者discipline v/n.纪律; 学科；训练;prince n.王子princess n.公主principal a.首要的principle n.原则;主义participate v.(in)参与；分享participant n.参与者a.参与的municipal a.市的；市政的sec-/sequ-跟着second a.第二的，随后的prosecute v.起诉vi.作检察官prosecutor n.检察官prosecution n.控告，起诉subsequent a.随后的execute v.执行死刑;执行execution n.执行，executive n.总经理a.执行的consequence n.结果,意义,影响consequently ad.结果，因此consecutive a.连续的persecute v.迫害sequence n.秩序rect-词根：直right a.正确的，直的erect v.勃起；竖起direct a.直接的direction n.方向director n.总监；导演rectify v.纠正sume-词根：抓、摘、揪presume v.假设；臆测；猜presumably a.假设的resume n.简历v.重新开始buffet n.自助餐recipe n.食谱canteen n.餐厅；小卖部china 瓷器tornado n.龙卷风tsunami n.海啸;seismic adj.地震的;consume vt.消耗；吃完，喝光consumption n.消费assume vt.假设；承担;采取summary n.摘要，概要;adj.概括的，总结的; summarize v.(summarise)概括,总结cise-/cide-词根：切precise adj. 清晰的；精确的；precisely adv.精确地；恰好地；decide v.决定；决断decisive adj.决定性的; 坚定的; 果断的decision n.决定,决心;决议;决策incise vt.（在表面）雕，刻;excise v.切除concise a.简短的scissors n.剪刀suicide v.自杀pesticide n.杀虫剂serv-词根：保存save v.保存preserve v.保鲜；保存deserve v.应得；应受reserve v.保留;预定reservation n.保留;预定reservoir n.水库conserve v.保存，保全；保守conservative a.保守的conservation n.保存servant n.奴隶；奴仆serve v.服务service n.服务;公共设施; v.维修sid-词根：坐sit v.坐preside v.(at,over)主持president n.总统,校长,会长,主席subside v.平息；安抚subsidy n.补助金；津贴费subsidize vt.给…补助;inside a.里面的ad.在里面n.内部prep.在…里insidious a.暗中危害的reside v.居住resident adj.定居的n.居民;residence n.住所assiduous adj.刻苦的;struct-词根：建造destroy v.毁坏instruct v.教授;指导;instructor n.指导者，教师;instruction n.教育instructive a.有教育意义的construct v.建造construction n.建筑structure n.结构obstruct v.阻碍hibit-词根：拿prohibit v.禁止inhibit v.抑制exhibit v.展览exhibition n.展览cogn-词根：知道recognize v.认出cognition n.认知学cognitive a.认知的flect-/flex-词根：弯曲flexible a.灵活的；柔韧的reflect v.反射；反响；反应；反思flat a.扁平的path-词根：情感passion n.激情，感情sympathy n.同情sympathetic a.同情的pathetic a.可怜的compassion n.怜悯，同情; 恻隐之心;unit5nounce-词根：知道know v.知道pronounce v.宣告；发音pronunciation n.发音;pronounced a.明显的denounce vt.公开抨击announce v.宣告oper-词根：做labor n.n.劳动；努力；工作；劳工; operate v.手术；操作；运转cooperate v.合作cooperation n.合作cooperative a.合作的operate v.操作operation n.操作operational a.操作的sert-词根：插入insert v.插入desert v.遗弃n.沙漠assert v.断言；宣城exert v.施加（影响力）chron-词根：时间clock n.钟，表chronic a.慢性的，积习难改的chronicle n/v.编年史；历史colonize v.殖民地chronology n.年代学; 年表patronize v.屈尊;摆出高人一等的派头chronological adj.编年的;年代的synchronize v.同时；同步;mens-/mend-词根：测量metre n.米v.测量immense adj.巨大的;dimension n.尺寸; 维度；范围; mand-词根：命令demand v/n.需求command v.命令mandate v.命令；授权tract-词根：拉扯drag v.拽tractor n.拖拉机attract v.吸引distract v.分散注意力portray v.绘画；扮演（角色）; portrait n.肖像trait n.特征subtract v.扯走；减去extract v.拔出retreat v.撤退；退却contract v.达成共识；收缩；感染n.合同distress v.使痛苦attraction n.吸引力attractive a.有吸引力的t rigger n.扳机v.触发strict a.严格的；严厉的port-词根：运输port n.港口support v.支持import v.进口report v.报道reporter n.记者transport v.运输porter n.搬运工portable a.便携的export v.出口liber-词根：自由illiberal a.狭隘的liberal a.自由的liberate v.使自由；解放deliberate a.蓄意的liberty n.自由cred-信credit card n.信用卡incredible a.难以置信的credible a.可信的credit n.信誉；学分creditor n.债主；债权人debtor n.债务人credentials n.资格证书credential n.凭证；国书;her-/hes-词根：粘coherent a.连贯的cohesive a.凝聚力的；团结的adhere v.黏贴；坚持stick v.黏贴；坚持hesitate v.犹豫pet-喜爱，追求pet n.宠物compete v.竞争competent a.有能力的competitive adj.竞争的competition n.竞争petal n.花瓣perpetuate vt.使永久perpetual a.永久的petition n.请愿书; 请愿。

细胞逆转录转座子及其功能研究细胞逆转录转座子（LTRs）是一类特殊的转座子，它们在细胞DNA中构成了很重要的基因组组成元件。

转座子是可以改变基因排列和表达的DNA序列，因此在基因组进化和调控中具有至关重要的作用。

在本文中，我将深入探讨细胞逆转录转座子及其功能研究。

一、逆转录转座子的概述逆转录转座子（retrotransposon）是由RNA媒介的“逆向反录”过程使DNA复制插入到基因组中的移动元件。

它们是真核生物基因组中的最重要的复制性基因组元件之一。

逆转录转座子在细胞中存在不同的亚型，主要分为长镜像转座子（LTRs）和非长镜像逆转录转座子（non-LTRs）。

其中，LTRs是带有长镜像序列的逆转录转座子，能与终端重复序列（terminal repeat sequences）配对形成类似病毒颗粒的粒子，是目前已知的大部分逆转录转座子的一种。

二、LTRs的结构和功能LTRs由内部反向转录（reverse transcription）酶、内部RNA转录起始位点（promoter）和长镜像序列组成。

内部反向转录酶可转录，逆转录RNA并将其插入到新的位点中。

内部RNA转录起始位点能驱动LTR的转录，这样它们就能制造足够数量的RNA，并使它们转录逆行后转化为DNA。

而长镜像序列则起到了重要的调控作用，包括DNA复合物的形成，RNA转录和后转录活动的调节。

虽然细胞逆转录转座子的具体功能还不是很清楚，但是它们已经被发现对基因调控和表达具有重要的影响。

例如，有些LTRs可以充当编码转录因子（transcription factor）的端点，从而控制基因表达和调节。

此外，LTRs也可能影响DNA复制、修复和重组过程，从而对细胞的遗传稳定性产生影响。

三、LTRs的研究进展随着分子生物学和基因组学的进步，LTRs的研究进展迅速。

目前已经有大量的研究表明，LTRs在多种生物体中广泛分布，是基因组演化和调控的重要组成部分。

分⼦⽣物学第三章RNA转录第三章 RNA 转录(RNA transcription)3.1. Basic concept3.2. Trancription survey3.3. Promoter in Eukaryotes and Prokaryotes3.4. Transcription Termination3.5. Pre-RNA processing in Eukaryotes3.1. 基本概念（P64） Basic concept●基因表达的第⼀步●以D. S. DNA 中的⼀条单链作为转录的模板某⼀基因只以⼀条单链DNA 为模板进⾏转录（不对称转录）●在依赖DNA 的RNA 聚合酶的作⽤下●按A U ，C G 配对的原则，合成RNA 分⼦●模板单链 DNA 的极性⽅向为3’ → 5’, ⽽⾮模板单链DNA 的极性⽅向与RNA 链相同，均为5’ → 3’.● RNA 的转录包括promotion, elongation, termination 三个阶段●从启动⼦（promoter ）到终⽌⼦（terminator ）的DNA序列称为转录单位（transcriptional unit ）●原核⽣物中的转录单位多为 polycistron in operon真核⽣物中的转录单位多为monocistron, No operon●转录原点记为+1，其上游记为负值，下游记为正值● RNA 的主要种类及功能：mRNA ——携带编码多肽的遗传信息tRNA ——将核苷酸信息转化为aa 信息转运aa 进⼊核糖体rRNA ——参与多肽合成3.2.RNA 转录概况3.2.1转录的基本过程1. 模板识别：RNApol 与启动⼦相互识别并结合的过程（形成封闭的⼆元复合物）启动⼦（promoter ）：DNA 分⼦上结合RNApol 并形成转录起始复合物的区域，通常也包括促进这⼀过程的调节蛋⽩结合位点rich A/T ，易发⽣DNA 呼吸现象形成单链区2转录起始：启动⼦区解链，转录起始（封闭的⼆元复合物开放的⼆元复合物三元复合物）通常在这⼀过程中RNApol 移动较慢，且易发⽣脱落——流产式起始 ——决定启动⼦的强弱3延伸：延伸过程中的延宕现象（Eukaryotes ）：Euk genome G/C 分布不均匀σ脱离全酶（Pro ）/RNApol 脱离转录起始复合物（Euk ）4终⽌：在终⽌⼦（terminator ）处停⽌转录3.2.2 RNApolymerase1 RNA polymerase in Prokaryotes （以E.coli 为例）1）构成核⼼酶(core enzyme)：2αββ’DNA3’----TACTCAT----5’ RNA 5’----AUGAGUA----3’5’---ATGAGTA----3’ Non-template (sense strand)template (antisense strand)全酶（holoenzyme)2αββ’σα：核⼼酶组建因⼦/ 启动⼦识别β：RNA合成的活性中⼼β’：与β共同构成活性中⼼σ：识别启动⼦，增加酶与DNA的亲和⼒σ因⼦可减少RNApol与⾮启动⼦DNA序列的亲和⼒，⽽增加RNApol与启动⼦的亲和⼒，⼀旦转录起始，σ因⼦将脱离RNApol再次引导新的RNApol进⾏转录ρ：参与转录终⽌2）Rifamycin（利福霉素）及Streptolydigin（利链菌素）对Pro转录的影响Rif可结合β，阻⽌NTP的进⼊I位点（Initiation site )（⼀旦形成三元复合物Rif不再起抑制作⽤）；利链菌素结合β的延伸位点(Elongation site)，抑制延伸。

Initiation of transcription1 IntroductionTranscription in eukaryotic cells is divided into three classes. Each class is transcribed by a different RNA polymerase:•RNA polymerase I transcribes rRNA•RNA polymerase II transcribes mRNA•RNA polymerase III transcribes tRNA, 5SrRNA and other small RNAs.The general factors are required for the mechanics of initiating RNA synthesis at all promoters.•join with RNA polymerase to form a complex•determine the site of initiation.•The general factors together with RNA polymerase constitute the basal transcription apparatus.•The upstream factors are DNA-binding proteins that recognize specific short consensus elements located upstream of the startpoint. They increase the efficiency of initiation, and are required for a promoter to function at an adequate level.•The inducible factors function in the same general way as the upstream factors, but have a regulatory role. They are synthesized or activated at specific times or in specific tissues, and they are therefore responsible for the control of transcription patterns in time and space. The sequences that they bind are called response elements.•The promoters for RNA polymerases I and II are (mostly) upstream of the startpoint•Some promoters for RNA polymerase III lie downstream of the startpoint.•Each promoter contains characteristic sets of short conserved sequences that are recognized by theA typical gene transcribed by RNA polymerase IIhas a promoter that extends upstream from the sitewhere transcription is initiated. The promotercontains several short (<10 bp)sequence elementsthat bind transcription factors, dispersed over >200 bp. An enhancer containing a moreclosely packed array of elements that also bindtranscription factors may be located several kb distant.Enhancer element is a cis-acting sequence thatincreases the utilization of (some) eukaryotic promoters,(upstream or downstream) relative to the promoter.it inhibits transcription by certain eukaryotic RNA polymerases, especially RNA polymerase II.•All eukaryotic RNA polymerases are large proteins, appearing as aggregates of >500 kD. They typically have 8~14 subunits.•The purified enzyme can undertake template-dependent transcription of RNA, but is not able to initiate selectively at promoters.•The three largest subunits have homology to βand β’ subunits of bacterial RNA polymerase. •Three of the remaining subunits are common to all the RNA polymerasespolymerase II has a carboxy-terminal domain (CTD), which consists ofyr-Ser-Pro-Thr-Ser-Pro-SerThere are ~26 repeats in yeast and ~50 in mammals. The number of repeats is important,threonine res idues, which is involved in theInitiation via the internal pol III promoters involves the assembly factors TFIIIA and TFIIIC, the initiation factor TFIIIB, and RNA polymerase III.Promoters for RNA polymerase III may consist of bipartite sequences downstream of the startpoint, with boxA separated from either boxC or boxB. Or they may consist of separated sequences upstream of the startpoint(Oct, PSE, T ATA).• In both cases, the binding of TFIIIC in turn enables TFIIIBto bind to a sequence surrounding the startpoint.• TFIIIA and TFIIIC are assembly factors , TFIIIB functions as a "positioning factor," responsible for localizing RNA polymerase correctly. Like SL1 at the pol I promoter.• and also in the corresponding transcription factor (TFIID)for RNA polymerase II • The upstream elements function in a similar manner in promoters for both polymerases II and III. •Initiation at an upstream promoter for RNA polymerase III can occur on a short region thatimmediately precedes the startpoint and contains only the TA TA element.• However, efficiency of transcription is much increased by the presence of the PSE and OCT elements. • eukaryotic transcription describes the assembly of transcription factors at the promoter before RNA polymerase binds.• For the type 1 and type 2 internal promoters, the assembly factors ensure that TFIIIB (which includes TBP) is bound just upstream of the startpoint, to provide the positioning information.• For the upstream promoters, transcription factors that directly recognize the upstream sites form a complex (including TBP) that is recognized by RNA polymerase III.5。

Leading Edge PreviewsCell 132, March 21, 2008 ©2008 Elsevier Inc. 917Intrinsic terminators for E. coli RNA poly-merase, also known as simple or factor-independent terminators, were the first to be discovered and soonbecame prototypes for themost abundant class of termi-nators in Eubacteria. They areused both to signal transcrip-tion termination at the ends ofoperons and as control ele-ments in the attenuators andriboswitches that are founddownstream of the promot-ers of a variety of bacterialbiosynthetic operons. Intrinsicterminators consist of a hair-pin structure followed by a 7–9nucleotide U-tract, sometimesinterrupted by one or moreother residues, at the 3′ endof the RNA (see Figure 1A),and many experiments haveshown that these features areessential for the functioning ofthese terminators (Nudler andGottesman, 2002).As their name suggests,intrinsic terminators are recog-nized directly by the multisub-unit bacterial RNA polymerasecore enzyme. Although thepath of nucleic acids within the structure of an RNA poly-merase elongation complex has been determined (Korzheva et al., 2000), it has not been easy to understand either the energetics or the mechanism of transcription termination. In this issue of Cell , Larson et al. (2008) describe the use of single-molecule assays involving optical traps to monitor elongation through intrinsic terminators. By attaching RNA polymerase and either one end of its DNA template (Figure 1B) or the 5′ end of its nascent RNA transcript(Figure 1C) to different beads, this assay allows force to be applied between the RNA poly-merase molecule and either its template or its transcript. The results of this analysis have deepened our understanding of the functioning of these ter-minators.Because the RNA:DNA hybrid in the transcription bubble is 9 bp long (Gnatt et al., 2001), it consists entirely (or almost entirely) of rU:dA base pairs at the termina-tion site. The presence of the U-tract is sufficient to cause RNA polymerase to pause (Gusarov and Nudler, 1999; Yarnell and Roberts, 1999), thereby providing a kinetic window for termination. The rU:dA hybrid is also particu-larly weak, and weak hybrids have the potential to cause RNA polymerase to back-track, moving the 3′ end of the RNA away from the catalytic center of RNA polymerase and into its secondary chan-nel (Nudler and Gottesman, 2002). However, backtracking should not promote dissocia-tion of the elongation complex because the RNA:DNA hybrid would become stronger, notweaker. In any case, back-Transcription Termination:Pulling Out All the StopsJack F . Greenblatt 1,*1Banting and Best Department of Medical Research and Department of Molecular Genetics, Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, 160 College Street, Toronto, ON, Canada M5S 3E1*Correspondence:***************************DOI 10.1016/j.cell.2008.03.003In this issue, Larson et al. (2008) describe the use of optical traps to pull on the DNA template or RNA transcript and thereby explore the termination mechanism for E. coli RNA polymerase at intrinsic terminators. Their results imply that, depending on the nature of the terminator sequence, RNA polymerase uses either hypertranslocation or RNA:DNA shearing to destabilize the hybrid inthe transcription bubble.Figure 1. Single-Molecule Analysis of Intrinsic Terminators (A) Structures of three intrinsic terminators illustrating their characteristic RNA hairpins and U-tracts. The bases where termination occurs are underlined.(B) Experimental set-up for the DNA-pulling assay (Larson et al., 2008). RNA polymerase (green) and one end of its DNA template (dark blue) are attached to different polystyrene beads (light blue) suspended in two separate optical traps (orange). The nascent RNA (red) is untethered. The arrow indicates the direction of transcription. In this orientation, the applied force assists translo-cation by RNA polymerase.(C) Experimental set-up for the RNA-pulling assay. In this case, the nascent RNA is tethered to one of the beads via hybridization to a DNA handle.tracking may be inhibited by the pres-ence of the RNA hairpin. Consistent with this expectation, Larson et al. found that application to the RNA polymerase of a hindering force along the DNA to assist backtracking did not generally affect ter-mination in their assay.The RNA hairpin that precedes the U-tract has a key role in termination. There is evidence that formation of the base of the hairpin somehow leads to disruption of the upstream portion of the hybrid, weakening the hybrid and thereby facilitating termination (Gusarov and Nudler, 1999; Yarnell and Roberts, 1999; Komissarova et al., 2002). Indeed, interaction between the hairpin and RNA polymerase is stabilized by the elonga-tion factor NusA, which increases RNA polymerase pause times at hairpin-dependent pause sites and increases the efficiencies of intrinsic terminators (Nudler and Gottesman, 2002). Consis-tent with expectations, Larson et al. found that termination was inhibited when suf-ficient force was exerted on the 5′end of the nascent RNA so as to begin dis-rupting the hairpin. However, one of the curiosities of their study is that exertion of a lesser force on the RNA increased the efficiency of termination. They used single-stranded DNA molecules comple-mentary to the transcript to show that this is apparently caused by the forma-tion in the upstream RNA of weak sec-ondary structures that compete with the formation of the terminator hairpin.In principle, a different way to shorten and weaken the RNA:DNA hybrid is the forward translocation by RNA poly-merase in the absence of concomitant RNA synthesis. It has been shown previ-ously that RNA polymerase hypertrans-location is an important component of the termination mechanism at the t500 intrinsic terminator (derived from bac-teriophage φ82) (Santangelo and Rob-erts, 2004). When Larson et al. applied an assisting or hindering force to the RNA polymerase (as shown in Figure 1B), the kinetics of release were altered for t500 and the termination efficiency was altered for a hairpin mutant of t500. Moreover, the optical trap data for t500 predicted hypertranslocation by severalnucleotides, consistent with the find-ings of Santangelo and Roberts (2004).Assisting or hindering forces did not,however, affect the efficiencies for twoother intrinsic terminators, his (from theattenuator of the E. coli his operon) andtR2 (from bacteriophage λ), indicatingthat these terminators, unlike t500, donot apparently use hypertranslocation toweaken the hybrid.How then does release occur at theseother terminators? Larson et al. foundthat applying tension between the RNA 5′end and the RNA polymerase (as shownin Figure 1C) led to sequence-dependentrelease at the U-tract. In this case, theypropose that the event that leads to ter-mination is shearing of the RNA:DNAhybrid by about 1 bp. Because shearingshould be energetically more favorablefor terminators containing pure U-tracts,like his (Figure 1A, left), or perhaps onlyone non-U residue, like tR2 (Figure 1A,right), and less favorable for t500 (Figure1A, middle), which contains two non-Uresidues in its U-tract, this may explainwhy t500, unlike the other terminators inthis study, requires hypertranslocationby RNA polymerase. Hypertransloca-tion requires melting of the DNA aheadof the termination site. Therefore, thishypothesis is also consistent with previ-ous observations that the sequence ofthe DNA ahead of the U-tract specificallyaffects termination when the sequencedownstream of the hairpin containsmultiple non-U residues (Reynolds andChamberlin, 1992).Exerting force on the DNA or RNA isexpected to alter the energy landscapefor termination if the termination eventrequires motion of the RNA polymerasewith respect to one or other nucleic acid.As a consequence, Larson et al. wereable to use their data to derive a quan-titative model that predicts terminationefficiency as a function of the sequencesand predicted stabilities of the RNAhairpin and RNA:DNA hybrid. Pulling onthe RNA with sufficient force to dissoci-ate the closing base pairs of the hairpinreduced the termination efficiency. Theypostulate that it is the closing of thesebase pairs that generates the signalthat leads to forward translocation orshearing of the hybrid (or both), as wellas disruption of the upstream portion ofthe hybrid, and the energy that makesthem possible. A short rU:dA hybridwould dissociate spontaneously if notfor its stabilization by contact with RNApolymerase (Gnatt et al., 2001), imply-ing that RNA polymerase would have adirect role in the shearing mechanism.Given that the base and loop of thehairpin are located far from the catalyticcenter of RNA polymerase and mostof the hybrid, transmission of this sig-nal must involve allosteric movementswithin RNA polymerase that ultimatelyalter its contacts with the hybrid andlead to melting or shearing of the hybridor hypertranslocation. It is known thata specific contact between the hairpinand the flap domain of RNA polymeraseis required for the functioning of hairpinpause sites (Toulokhonov et al., 2001).Exactly how the hairpin of an intrinsicterminator causes an allosteric signal tobe transmitted within RNA polymeraseto promote termination is an importantsubject for future investigation.ReFeRenceSGnatt, A.L., Cramer, P., Fu, J., Bushnell, D.A., andKornberg, R.D. (2001). Science 292, 1876–1882.Gusarov, I., and Nudler, E. (1999). Mol. Cell 3,495–504.Komissarova, N., Becker, J., Solter, S., Kireeva, M.,and Kashlev, M. (2002). Mol. Cell 10, 1151–1162.Korzheva, N., Mustaev, A., Kozlov, M., Malho-tra, A., Nikiforov, V., Goldfarb, A., and Darst, S.A.(2000). Science 289, 619–625.Larson, H., Greenleaf, W.J., Landick, R., andBlock, S.M. (2008). Cell, this issue.Nudler, E., and Gottesman, M.E. (2002). GenesCells 7, 755–768.Reynolds, R., and Chamberlin, M.J. (1992). J. Mol.Biol. 224, 53–63.Santangelo, T.J., and Roberts, J.W. (2004). Mol.Cell 14, 117–126.Toulokhonov, I., Artsimovitch, I., and Landick, R.(2001). Science 292, 730–733.Yarnell, W.S., and Roberts, J.W. (1999). Science284, 611–615.918Cell 132, March 21, 2008 ©2008 Elsevier Inc.。

——“水映天，天接地，人在湖间走，宛如画中游。

”«L’eau reflète le ciel, et le ciel se joint à la terre;les gens marchent entre les eaux du lac, comme s’ilsnageaient dans une peinture.»这是茶卡盐湖的真实写照。

凡去过茶卡盐湖的人，都会为这样一幅美不胜收的“山水画”魂牵梦萦。

Telle est une véritable description du lac saléChaka. Quiconque a visité le lac verra son esprit hantépar cette «image de paysage» magnifique.茶卡盐湖位于青海柴达木盆地的边缘，面积约105平方公里，是世界上盐储存量最大的内陆湖。

这里平均海拔3 059米，气候凉爽，常年干旱少雨。

从高处俯视，整个湖夹在祁连山支脉完颜通布山和昆仑山支脉旺尕秀山之间，山上的积雪倒映在湖面上，形成了水天相接、盐湖与雪山相融的独特雪域风光。

Le lac salé Chaka est situé au bord du bassin deQaidam dans le Qinghai. Il couvre une superficie—————作者：樱花飘落 Yinghua Piaoluo翻译：王文新 Wang Wenxin d’e nviron 105 kilomètres carrés et il est le lac intérieur qui contient le plus de sel au monde. Avec une altitude moyenne de 3 059 mètres, il a un climat frais et sec, avec peu de précipitations tout au long de l’année. En regardant d’en haut, le lac entier est pris en sandwich entre une branche de la montagne Qilian, le mont Wanyan Tongbu, et une branche de la montagne Kunlun, le mont Wanggaxiu. La neige sur les montagnes se reflète dans l’e au du lac, formant un paysage unique où l’e au et le ciel se rencontrent, et le lac salé et les montagnes enneigées se confondent.“茶卡”是藏语，意思是“盐池”，其蒙古语为“达布逊淖尔”，也就是青盐的海。

2021刘一男词根词缀完整笔记-手工版-CAL-FENGHAI.-(YICAI)-Company One1unit1ripe n.成熟rip v.裂口rupt-词根：破interrupt v.打搅，打断corrupt v.贿赂a.腐败的corruption n.腐败; 贪污; 贿赂;erupt v.（火山）爆发disrupt v.崩溃；瓦解rupture n.破裂claim-词根：喊叫proclaim v.宣城scream v.尖叫exclaim v.呼喊reclaim v.要求归还acclaim v.欢呼；喝彩claim v.要求；声称verse-vert-词根：旋转invert v.倒置,倒转,颠倒avert v.躲避；转移convert v.皈依；兑换；变换divert v.转向diversion n.转向verse-词根：旋转reverse n.相反;背面 a.相反的 v.颠倒,倒转adverse a.不利的，有害的conversely ad.相反地conversation n.会话,谈话verse n.诗节prose n.散文universe n.宇宙universal a.普遍的;宇宙的university n.(综合)大学controversial a.引起争议的controversy n.争议diverse a.多种多样的,(from)不同的diversion n.转向,转移;牵制;解闷;娱乐divorce v./n.离婚,分离version n.版本;译本,译文;说法edition n.版本（编辑的）versatile a.多才多艺的；多功能versus prep.对抗inverse a.相反的quiver v.颤抖sist-站subsistence n.维持生计insist vi.(on)坚持要求exist v.存在;existence n.存在resist v.抵制resistant a.抵制的resistance n.抵制transistor n.晶体管consist v.(in)存在于;(of)由…组成,由…构成consistent a.(in)前后一致的；（with）一致，符合persist v.持久persistent a.持久的stand v.站assist vt.协助assistant n.助理assistance n.协助dict-说contradict v.反驳contradiction n.反驳predict v.预测diction n.语言dictionary n.字典dictate v.命令dictator n.独裁者indicate v.暗示；表明indication n.暗示；表明indicator n.指数indicative a.表明的addict n.上瘾的人a.上瘾的addiction n.上瘾verdict v.裁定very a.非常的；真正的doc-词根：写下来document n.文件documentary a.文件袋n.纪录片orthodox n.正统的，东正教的paradox n.悖论；矛盾pose-放propose v.建议；求婚proposal n.建议；求婚proposition n.建议suppose v.假设supposal n.假设deposit v.沉淀；存款impose v.强迫；征税expose v.暴露exposure n.暴露compose v.组成；作文；作曲composite a.组成的composition n.组成；作文；作曲composure n.镇静，沉着;pose n.姿势v.摆放posture n.姿势put v.放dispose v.处理；处置disposal n.处理；处置disposable a.可降解的；一次性的positive a.确定的；积极的；肯定的pending a.不确定的penis n.阴茎position n.位置; 地位，职位;post n.邮局；岗位v.张贴opposition v.反对possess v.占有possession n.占有；占有物obsess v.着迷，萦绕obsession n.着迷，萦绕purpose n.目标preposition n.介词spect-看spy n.间谍 v.偷inspect v.检查inspector n.检察员retrospect v./n.回顾；追溯[反]foresee perspective a.透视的n.透视图;观点introspect v.内省respect v.尊敬；尊重respectable a.可敬的respectful a.毕恭毕敬的irrespective a.不考虑的respective a.各自的prospect n.前景spectator n.观众spectacle n.奇观spectacular a.奇观的specimen n.样品speculate v.推测，投机calculate v.计算; 估计;aspect n.方面；外貌respect v.尊敬suspect v.怀疑suspicion n.怀疑suspicious a.怀疑的sceptical a.怀疑论的；怀疑主义的skeptical a.怀疑论的；怀疑主义的despite prep.尽管despise v.鄙视expect v.期盼expected a.期待的unexpected a.始料未及的conspicuous a.有目共睹的press-压pressure n.压力suppress v.镇压（运动）depress v.压抑（情感）depressed a.压抑的impress v.给…深刻印象（褒义词）impressive a.令人印象深刻的impression n.印象express v.表达n.特快专递expression n.表达expressive a.表达的repress v.抑制（情感）compress v.压缩compressed a.压缩的compression n.压缩pressure n.压力fact-fect-fict-词根：做factory n.工厂，制造厂factor n.因素facile a.容易做的（对付事儿的）facility n.容易facilitate v.使容易facilitator n.援助者fact v.事实exact a.确切的exactly ad.确切地unit2fect-f词根：做defect n.瑕疵；缺点infect v.感染；传染infection n.感染；传染infectious a.感染的；传染的effect n.效果；结果effective a.有效果的efficient a.效率高的;perfect adj.完美的;affect vt.影响(疾病)；感动affection n.疾病；感情suffice v.足够sufficient a.(for)足够的deficient a.不足的deficiency n.缺失deficit n.亏损art n.艺术；技术artificial a.造作的；人造的profit n.利润profitable a.有利可图的fer-词根：运输、携带prefer v.更喜欢preference n.更喜欢；偏好suffer v.遭受infer v.推论inferior a.次要的defer v.屈尊；耽搁deference n.屈尊；耽搁refer v.提及；参考refer to 指的是transfer vt./n.转移；转换；过户；改乘confer v.授予conference n.(正式)会议differ v.不同difference n.不同interfere v.(in)打搅；干扰;intervene v.干涉；干预interference n.(in)打搅；干扰;ferry v.摆渡fertile adj.肥沃的; 可繁殖的; fertilize v.施肥fertilizer n.肥料fertilization n.施肥offer v.提供n.机会metaphor n.隐喻ferrycarry v.运输tain-拿contain v.包含，容纳container n.容器content n.内容a.满意的take v.拿sustain vt.支撑sustainable a.可支撑的sustainability n.可持续的detain v.扣押；耽搁retain v.保留retention n.记忆力attain v.（经过努力）达到protein n.蛋白质vitamin n.维生素; 维他命;insulin n.胰岛素;pertain v.有关pertinent a.相关的entertain v.招待；娱乐entertainment n.娱乐maintain v.维持；持有观点maintenance n.维持obtain v.获得tennis n.网球scribe-写rub v.擦，摩擦rubber n.橡胶; 橡皮;catch v.抓scratch v.挠prescribe v.指示；规定；开处方prescription n.处方subscribe v.签署同意；订阅；认捐subscription n.订阅；认捐describe v.描述；描写description n.描述；描写inscribe v.题；刻transcribe v.誊写; 改编transcription n.誊写ascribe v.归…于script n.手稿tect-盖子detect v.发现detective a.发现的n.侦探detection n.发现protect v.(from)保护,保卫sect-切section n.部分insect n.昆虫intersection n.十字路口sector n.部门，部分；section n.部分; 节; vi.切开; segment n.段,片,节,部分segregate v.隔离execute v.执行;执行死刑executive a.执行的n.总经理execution n.执行plex-/plic-叠x-象形implicit a.含蓄的explicit a.坦率的complicate v.使复杂complicated a.错综复杂的perplex v.使困惑surplus a.过剩的,剩余的replicate v.折叠；复制duplicate v.折叠；复制ply-词根：叠supply v.(with,to)供给,供应,supplyer n.供应商imply v.暗示；含蓄implication n.意义；含义reply v.回答comply v.遵守；服从compliance n.遵守；服从compliment n./v.称赞,恭维apply v.申请；应用application n.申请；应用applicable adj.适当的; 可应用的;gress-词根：行走progress n/v.进步progressive a.进步的,先进的;前进的regress v.倒退；回归；退化regression n.衰退；回归；退化congress n.(代表)大会;(美国等国的)国会,议会congressional a.国会的; 议会的; aggressive a.侵略的，好斗的，有进取心的aggression n.上进心transgress v.越轨；违背（道德）digress v.偏题，miss-投、射promise v.承诺n.希望promising a.有希望的compromise v.妥协；损害submit v.递交；投降submission n.递交；投降transmission n.转播；传递；转发commission n.委员会;委任,emission n.发射（废气）dismiss v.解散；解雇；驳回missile n.导弹a.可投射的mission n.使命missionary n.传教士message n.信息messenger n.信使mit-投、射submit v.递交；投降transmit vt.转播；传送commit v.委托;犯(罪)committee n.委员会,全体委员emit vt.排放（废气）;发表;发行intermittent a.间歇的,断断续续的omit v.漏掉fess-说professor n.教授profession n.表白；宣布；文职professional a.职业的n.专业人员prophet n.预言家;prophecy n.预言;professor n.教授confess v.坦白; 忏悔fess v.坦白，供认unit3form-词根：形状、形成transformer n.变形者deform v.使变形（破坏）inform v.(of,about)通知informed a.消息灵通的information n.通知,报告;情报,资料,消息;信息reform v./n.改革,改造,改良transform vt.变形；变化;变压;conform vi.(to)遵守perform v.完成；表现;表演performer n.表演者performance n.表演,表现；性能uniform n.制服form n.形状,形式;表格 v.组成,构成;形成formal a.正式的;形式的formula n.(pl.formulae)公式;规则; formulate v.用公式表达；清晰的表达voc-词根：声音voice n.声provoke v.挑动provocation n.挑衅；招惹；激怒provocative a.挑衅的；招惹的advocate vt.鼓吹，提倡n.提倡者naïve adj.幼稚的；天真的；单纯的;vocable n.词vocabulary n.词汇,词汇量;词汇表vocal a.声音的vocation n.召唤;天职;职业vow n.誓言; 郑重宣布;vt.& vi.起誓，发誓; 郑重宣告;vowel n.元音；母音;evoke vt.唤起(回忆、感情等)；引起vis-/vid-看visit v/n.访问,参观provide v.提供,准备,假设；规定provided conj.倘若,只要,假如provident adj.有远见的，节俭的; provision n.供应；条款;survey v./n.俯瞰;社会调查surveillance n.监控;invisible a.看不见的,无形的revise v.修订review v.复习preview v.预习visible a.看得见的vision n.视觉;远见;洞察力;visitor n.访问者；参观者visual a.视觉的oral a.口头的aural a.听觉的manual a.手工做的,体力的 n.手册,指南physical a.物质的；身体的;物理的visa n.(护照等的)签证;维萨信用卡 vt.签证evidence n.明显;显著;根据;证据;迹象evident a.明显的,明白的advice n.劝告，忠告，(医生等的)意见advise vt.忠告，劝告，建议；通知，告知envisage vt.正视; 想象;duce-词根：引导introduce v.介绍，引荐deduce v.演绎；推导，生产deduct v.扣除deductible a.可扣除的induce v.导致；引导reduce v.减少,reduction n.减少conduct n.行为v.操作conductor n.操作者；运行者semiconductor n.半导体educate v.教育,培养,训练education n.教育,培养,训练introduce v.介绍，引荐introduction n.介绍produce v.生产product n.产品production n.生产；总产量productive a.高产的reproduce v.繁殖;复制flu-词根：流flow v.流superfluous a.过剩的influence n.渗透力；影响力 v.影响influential a.有影响的n.有影响的人affluent a.富足的；富裕的n.富人flu n.流感fluent adj.流畅的; 流利的;fluid adj.流体的n.液体，流体; fluctuate v.浮动；起伏ject-投、射project n.方案,项目v.投射,投影subject n.主题;主体，实验对象v.受制于subjective a.主观的inject v.注射eject v.弹出reject v.拒绝adjective n形容词pel-词根：推palm n.手掌propel vt.推进propeller n.螺旋桨，推进器;impel v.推进expel vt.驱逐;repel vt.击退;compel v.强迫compulsory a.必须做的necessary a.必须的spir-词根：呼吸spirit n.精神inspire vt.鼓舞inspiration n.灵感respire v.呼吸conspire v.串通一气，合谋conspiracy n.密谋perspire v.排行aspire v.渴望；立志得到aspiration n.志向，抱负;volve-词根：旋转involve v.卷入,牵涉;包含evolve v.(使)发展;(使)进化evolution n.发展,进化revolt v.革命；反叛revolution n.革命;反叛revolutionary a.革命的,革新的 n.革命者revolve v.(使)旋转;思考envelope n.信封stit-词根：站stand v.站substitute v.(for)代替 n.代替品institute v.建立n.学院institution n.机构institutional a.机构的；制度的constitute vt.组成，任命；制定法律constitution n.宪法constitutional n.宪法的constituent a.组成的；选民curs-/cur-词根：跑course n.过程；v.快跑current n.气流；水流；电流currently ad.当前的currency n.货币occur v.发生concur v.同时发生recur v.再次发生（贬义词）incur v.招惹precursor n.先驱excursion n.远足；郊游course n.过程 v.快跑cede-/ceed-走precede v.领先precedent n.先例unprecedented a.史无前例的preceding a.领先的proceed v.继续proceeding a.继续的procedure n.程序succeed vi.成功；继承vt.接替；继…之后exceed v.超出concede v.让步；认输recede v.渐退unit4cess-词根：走process n.过程,工序v.处理procession n.处理success n.成功successful a.成功的succession n.继承successive a.继承的successor n.继承者excess n.超出a.超出的excessive a.超出的predecessor n.前任recession n.衰退access n.入口 v.接近accessory n.附件；同谋accessible a.可达到的concession n.让步；认输；迁就sent-词根：感觉sense n.感觉；理性essence n.本质,进化essential a.本质的,必须的esthetic adj.感觉上的; 美学的; 审美的; aesthetic a.(esthetic)美学的，美的artistic adj.艺术的; 有美感的; 风雅的resent vt.反感；厌恶;consent v.同感consensus n. 舆论; 一致同意sensible a.明智的sensitive a.感性的；敏感的sentiment n.情绪sentimental adj.伤感的; 多愁善感的;scent n/v.香味，气味; 嗅觉;sess-词根：坐sit v.坐assess vt.评估；征税；评价session n.(一届)会议,一段时间vac-空cave n.洞evacuate vt.撤离，疏散; 排泄;vacuum n.真空; 空白;vacant adj.空闲的；空缺的vacation n.休假,假期ceive-拿receive v.收到susceptible adj.易受影响的; 易受感染的; deceive v.欺骗,蒙蔽deceit n.欺骗，欺诈;receive v.收到reception n.接待conceive v.怀孕; 构思;concept n.概念，想法conception n.概念的形成perceive v.洞察；觉察；感知perception n.洞察；觉察；感知;cip-词根：拿receive v.收到recipient n.接受者a.收到的receipt n.收据，发票；收入;reciprocal a.互利的；互惠的mutual adj.共有的; 相互的(情感上的) disciple n.信徒；门徒；追随者discipline v/n.纪律; 学科；训练;prince n.王子princess n.公主principal a.首要的principle n.原则;主义participate v.(in)参与；分享participant n.参与者 a.参与的municipal a.市的；市政的sec-/sequ-跟着second a.第二的，随后的prosecute v.起诉 vi.作检察官prosecutor n.检察官prosecution n.控告，起诉subsequent a.随后的execute v.执行死刑;执行execution n.执行，executive n.总经理a.执行的consequence n.结果,意义,影响consequently ad.结果，因此consecutive a.连续的persecute v.迫害sequence n.秩序rect-词根：直right a.正确的，直的erect v.勃起；竖起direct a.直接的direction n.方向director n.总监；导演rectify v.纠正sume-词根：抓、摘、揪presume v.假设；臆测；猜presumably a.假设的resume n.简历v.重新开始buffet n.自助餐recipe n.食谱canteen n.餐厅；小卖部china 瓷器tornado n.龙卷风tsunami n.海啸;seismic adj.地震的;consume vt.消耗；吃完，喝光consumption n.消费assume vt.假设；承担;采取summary n.摘要，概要;adj.概括的，总结的; summarize v.(summarise)概括,总结cise-/cide-词根：切precise adj. 清晰的；精确的；precisely adv.精确地；恰好地；decide v.决定；决断decisive adj.决定性的; 坚定的; 果断的decision n.决定,决心;决议;决策incise vt.（在表面）雕，刻;excise v.切除concise a.简短的scissors n.剪刀suicide v.自杀pesticide n.杀虫剂serv-词根：保存save v.保存preserve v.保鲜；保存deserve v.应得；应受reserve v.保留;预定reservation n.保留;预定reservoir n.水库conserve v.保存，保全；保守conservative a.保守的conservation n.保存servant n.奴隶；奴仆serve v.服务service n.服务;公共设施; v.维修sid-词根：坐sit v.坐preside v.(at,over)主持president n.总统,校长,会长,主席subside v.平息；安抚subsidy n.补助金；津贴费subsidize vt.给…补助;inside a.里面的 ad.在里面 n.内部 prep.在…里insidious a.暗中危害的reside v.居住resident adj.定居的n.居民;residence n.住所assiduous adj.刻苦的;struct-词根：建造destroy v.毁坏instruct v.教授;指导;instructor n.指导者，教师;instruction n.教育instructive a.有教育意义的construct v.建造construction n.建筑structure n.结构obstruct v.阻碍hibit-词根：拿prohibit v.禁止inhibit v.抑制exhibit v.展览exhibition n.展览cogn-词根：知道recognize v.认出cognition n.认知学cognitive a.认知的flect-/flex-词根：弯曲flexible a.灵活的；柔韧的reflect v.反射；反响；反应；反思flat a.扁平的path-词根：情感passion n.激情，感情sympathy n.同情sympathetic a.同情的pathetic a.可怜的compassion n.怜悯，同情; 恻隐之心;unit5nounce-词根：知道know v.知道pronounce v.宣告；发音pronunciation n.发音;pronounced a.明显的denounce vt.公开抨击announce v.宣告oper-词根：做labor n.n.劳动；努力；工作；劳工; operate v.手术；操作；运转cooperate v.合作cooperation n.合作cooperative a.合作的operate v.操作operation n.操作operational a.操作的sert-词根：插入insert v.插入desert v.遗弃n.沙漠assert v.断言；宣城exert v.施加（影响力）chron-词根：时间clock n.钟，表chronic a.慢性的，积习难改的chronicle n/v.编年史；历史colonize v.殖民地chronology n.年代学; 年表patronize v.屈尊;摆出高人一等的派头chronological adj.编年的;年代的synchronize v.同时；同步;mens-/mend-词根：测量metre n.米 v.测量immense adj.巨大的;dimension n.尺寸; 维度；范围;mand-词根：命令demand v/n.需求command v.命令mandate v.命令；授权tract-词根：拉扯drag v.拽tractor n.拖拉机attract v.吸引distract v.分散注意力portray v.绘画；扮演（角色）;portrait n.肖像trait n.特征subtract v.扯走；减去extract v.拔出retreat v.撤退；退却contract v.达成共识；收缩；感染n.合同distress v.使痛苦attraction n.吸引力attractive a.有吸引力的t rigger n.扳机v.触发strict a.严格的；严厉的port-词根：运输port n.港口support v.支持import v.进口report v.报道reporter n.记者transport v.运输porter n.搬运工portable a.便携的export v.出口liber-词根：自由illiberal a.狭隘的liberal a.自由的liberate v.使自由；解放deliberate a.蓄意的liberty n.自由cred-信credit card n.信用卡incredible a.难以置信的credible a.可信的credit n.信誉；学分creditor n.债主；债权人debtor n.债务人credentials n.资格证书credential n.凭证；国书; her-/hes-词根：粘coherent a.连贯的cohesive a.凝聚力的；团结的adhere v.黏贴；坚持stick v.黏贴；坚持hesitate v.犹豫pet-喜爱，追求pet n.宠物compete v.竞争competent a.有能力的competitive adj.竞争的competition n.竞争petal n.花瓣perpetuate vt.使永久perpetual a.永久的petition n.请愿书; 请愿。

Transcribe中文使用说明Transcribe! 7.31.0 中文使用说明转录!帮助内容在窗户7.31版本版权?1998-2006七弦软件。

版权所有。

微软视窗媒体技术利用部分。

版权?1999 - 2002年的微软公司。

版权所有。

概述转录的!应用程序是一个助理的人有时候想找出一段音乐从记录,以写出来或者玩它自己。

通常的方法做这是使用CD或者反复听随身听生意各个位,用你的耳朵,你的大脑弄清正在发生的事情。

除非你是个乐感很强的人,那么你也需要一钢琴、吉他便于检查那个音符是哪个。

转录!不从根本上改变程序,但旨在提供的帮助使它更加方便、快捷的服务。

音乐是表现为滚动波形显示,你可以把标志物部分,措施和节拍和给那些条幅的名字,让你一直都知道你是怎么想的。

界面灵活播放和响应,比如你可以改变环路分,播放速度、沥青等而回放仍在继续。

“导航栏”给作品的全面了解和标记你下。

你可以点击它跳转到任何就说到了点子上。

多环能得救,并且召回。

有许多命令与选择和播放、和你可以控制它们从完全可配置的键盘的捷径。

你可以用各种各样的踏板控制回放如果你愿意的话,让各种操作——开始和停止播放,你的脚。

您可以设定“全球快捷方式——那就是,键盘快捷键,即使转录工作!不是积极的应用。

所以你可以用音乐记谱法包来写你的转录,同时还能够控制转录!只用来播放使用键盘(或者说确实踏板,如果你有任何的)。

其他特点:谱分析的特点能帮助识别安装、卸载、系统的要求系统要求彩色显示屏,至少一项决议,800 * 600视窗2000 / NT / XP,声卡。

转录!第7版也可用来苹果操作系统10.3.4或之后,Linux系统/ GTK。

如果你有一个更老的窗口(95 / 98 /我还是Mac(OS 7.5 - 10.2),你仍然可以经营转录!版本6这仍然可只要有需求。

参观七串网站的更多信息。

安装转录!如果你正在读这篇文章,你可能会已经安装它。

但对于完整性:转录!对于Windows分布作为一个self-installing执行(建造的Inno指导)很精彩。

DOI: 10.1126/science.1127422, 518 (2006);313 Science et al.Nikolay Zenkin Transcript-Assisted Transcriptional ProofreadingThis copy is for your personal, non-commercial use only.clicking here.colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to othershere.following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles): October 7, 2014 (this information is current as of The following resources related to this article are available online at/content/313/5786/518.full.html version of this article at:including high-resolution figures, can be found in the online Updated information and services, /content/suppl/2006/07/25/313.5786.518.DC1.htmlcan be found at:Supporting Online Material /content/313/5786/518.full.html#related found at:can be related to this article A list of selected additional articles on the Science Web sites /content/313/5786/518.full.html#ref-list-1, 12 of which can be accessed free:cites 24 articles This article 23 article(s) on the ISI Web of Science cited by This article has been /content/313/5786/518.full.html#related-urls 30 articles hosted by HighWire Press; see:cited by This article has been/cgi/collection/molec_biol Molecular Biologysubject collections:This article appears in the following registered trademark of AAAS.is a Science 2006 by the American Association for the Advancement of Science; all rights reserved. The title Copyright American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the Science o n O c t o b e r 7, 2014w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o mTranscript-AssistedTranscriptional ProofreadingNikolay Zenkin,1*Yulia Yuzenkova,1Konstantin Severinov 1,2,3*Fidelity of template-dependent nucleic acid synthesis is the main determinant of stable heredity and error-free gene expression.The mechanism (or mechanisms)ensuring fidelity of transcription by DNA-dependent RNA polymerases (RNAPs)is not fully understood.Here,we show that the 3¶end–proximal nucleotide of the nascent transcript stimulates hydrolysis of the penultimatephosphodiester bond by providing active groups and coordination bonds to the RNAP active center.This stimulation is much higher in the case of misincorporated nucleotide.We show that during transcription elongation,the hydrolytic reaction stimulated by misincorporated nucleotides proofreads most of the misincorporation events and thus serves as an intrinsic mechanism of transcription fidelity.The mechanism of transcription is high-ly conserved in all living organisms.In the RNAP elongation complex,the 3¶end of the nascent RNA can occupy a post-translocated,a pretranslocated,or a back-tracked state (Fig.1A).In each of these states,the RNAP active center performs different reactions,i.e.,the forward reaction of nucleoside triphosphate (NTP)addition or hydrolytic cleavage of the nascent RNA (Fig.1A).Catalysis by the RNAP active center depends on two Mg 2þions (1–7)that activate reacting groups and stabilize leav-ing groups during nucleophilic attack on the phosphorus (4,8).In cellular RNAPs,only one Mg 2þion (MgI)is bound tightly in the ac-tive center.The other Mg 2þion,MgII (2,4–7),is bound weakly,but its binding is stabilized by the triphosphate moiety of the incoming NTP (5).The hydrolytic transcript cleavage reaction,characteristic of pretranslocated and backtracked elongation complexes (9)(Fig.1A),is slow compared to the forward RNA polymerization reaction,presumably because of poor binding of MgII (4).Although the rate of misincorporation of nucleotides by RNAP is much slower than the rate of incorporation of correct nucleo-side 5¶-monophosphates (NMPs)(10,11),the relatively low selectivity of RNAP (12)makes misincorporation unavoidable,suggesting the existence of a proofreading mechanism.To define such a mechanism,12complexes with mismatched NMP at RNA 3¶end (misincorpo-rated elongation complexes,MECs)modelingall possible misincorporation events and 4correct complexes (correct elongation com-plexes,CECs)were assembled by means of 4DNA templates that differed from each other only by a base pair at the þ1register (corresponding to the transcript 3¶end)and 45¶end–labeled RNAs that were identical except for the 3¶-terminal base (13)(fig.S1).Complexes were assembled in the absence of Mg 2þand were therefore inactive.Upon addition of Mg 2þto MECs,RNAP efficiently cleaved the penultimate (P2)phos-phodiester bond.No P1(ultimate phospho-diester bond)(Fig.1A)cleavage was observed (Fig.1,B and C),suggesting that MECs are backtracked by 1base pair relative to the pretranslocated state (Fig.1A).Cleavage of P2was much slower in CECs than in the cor-responding MECs (Table 1),as expected for active,not backtracked,complexes.However,because no P1cleavage was observed in CECs (Fig.1,B and C),stabilization of the backtracked state in MECs cannot explain preferential P2cleavage,which was also observed with eukaryal and archeal RNAPs (10,14–17)and appears to be a general phenomenon.Noncomplementary NTPs bind in the RNAP E-site close to the active center and stimulate P1cleavage (4).Addition of nonhydrolyzable E to prevent any possibility of (mis)incorporation in the nascent RNA ^NTP analog APcPP A adenosine-5¶-E (a ,b )-methyleno ^triphosphate Z (Fig.1C),noncomplementary to the DNA template guanosine in register þ2,led to stimulation of P1cleavage in CECs.No such stimulation was observed in MECs,indicating that base-pairing of the RNA _s 3¶end is required for NTP-assisted cleavage.Noncomplementary NTPs also inhibited P21Waksman Institute,2Department of Molecular Biology and Biochemistry,Rutgers University,Piscataway,NJ 08854,USA.3Institute of Molecular Genetics,Russian Academy of Sciences,Moscow,123182Russia.*To whom correspondence should be addressed at Waksman Institute,190Frelinghuysen Road,Piscataway,NJ 08854,USA.E-mail:nicserzen@mail.ru (N.Z.);severik@(K.S.)Fig.1.Cleavage in misincorporated (MECs)and correct (CECs)elongation complexes.(A )Schematic representation of catalytic reactions character-istic of transcription elongation complexes in different states.The red circle represents the active center that contains two Mg 2þions.(B )MECs (lanes 1to 6,13to 24)and a corresponding CEC (lanes 7to 12)(with CMP at the RNA 3¶end as an example)were supplied with 10mM Mg 2þand incubated for various times at pH 7.9(40-C).For each MEC,the first letter indicates misincorporated 3¶NMP,and the correct nucleotide that it replaces is indicated in parentheses (fig.S1).(C )CECs and MECs [A-CEC and U(A)MEC are shown as examples]were supplied with 15mM Mg 2þand incubated for various times with or without 1mM noncomplementary nonhydrolyzable NTP (APcPP).REPORTS28JULY 2006VOL 313SCIENCE518cleavage in both CECs and MECs in a dose-dependent manner (Fig.1C).Noncomplemen-tary NTPs are known to bind in the so-called E-site of the RNAP active center,the same site where initial interaction of correct NTPs with RNAP occurs.To explain the inhibitory effect,we postulate that in backtracked com-plexes,the 3¶-terminal NMP also occupies the E-site (or an overlapping site,Fig.2)and activates P2cleavage in a way that is simi-lar to P1cleavage activation by noncomple-mentary NTP.Binding of NTP in the E-site displaces the transcript _s 3¶end and destabi-lizes the backtracked state,thus inhibiting P2cleavage.Noncomplementary NTP activates P1cleavage by stabilizing MgII through interac-tion with the b and g phosphates (4,5).Because these phosphates are absent in the 3¶-terminal NMP,MgII coordination and/or P2cleavage may be stimulated by the terminal NMP itself.This hypothesis predicts that Mg 2þdependence of P2cleavage,which reflects the complex affinity for MgII (4),should have a lower dissociation constant (K d )than the intrinsic (unassisted by non-complementary NTP)K d of P1hydrolysis (9100mM)(4).This expectation was fulfilled for both MECs and CECs (Table 1).The lowest apparent K d observed (8mM)is close to the K d of P1hydrolysis stimulated by noncomplementary NTP (4).Thus,the 3¶-terminal NMP,either matched or mismatched,increases the P2cleavage velocity by increasing affinity for MgII.A high rate of P2cleavage could not be solely due to a decreased K d for MgII,be-cause cleavage velocity at saturating Mg 2þconcentrations (k cat )differed depending on the nature of 3¶-terminal NMP (Table 1).For example,comparisons of complexes con-taining A,G,or U instead of correct C at the 3¶end (Table 1rows 2,7,and 15,cor-respondingly)reveal that the cleavage re-action k cat values in different complexes differ significantly (0.14,0.028,and 0.015s j 1,respectively).This suggests that some groups of the transcript _s 3¶-end NMPs par-ticipate,directly or indirectly,in cleavage.Whereas the k cat of P2cleavage in MECs is determined by the properties of the reaction itself,in CECs it is strongly influenced by base-pairing of the 3¶end with the template strand,which affects the probability of back-tracked state occupancy.To avoid this compli-cation,we focused on MECs only (supporting online text).High pH deprotonates the active water molecule stimulating phosphodiester hydroly-sis by the RNAP active center.The stimula-tion depends on the reaction mechanism and should plateau at a pH equal to the system p K value.Therefore,if mismatched nucleotides were involved in cleavage,different profiles of cleavage reaction dependence on pH are expected for different MECs.This expecta-tion was fulfilled (fig.S2).The shapes of pH curves were different from that of the previously reported P1cleavage curve (4)(dotted line in fig.S2),indicating that the mechanism of P2cleavage was distinct from intrinsic RNAP-catalyzed P1hydrolysis.Whereas most P2cleavage profiles pla-teaued at about pH 9.5,some had a different E U(C)MECs ^plateau or even double (A-MECs)plateaus.Thus,different acid/base systems provided by the transcript 3¶-terminal nucle-otide participate in P2cleavage in different MECs.The dependence of cleavage reaction properties for complexes containing misin-corporated cytidine 5¶-monophosphate (CMP)and uridine 5¶-monophosphate (UMP)on the þ1DNA template-strand base may be ex-plained by effects of local sequence-dependent deviations of nucleic acids structure near the active center on the reaction pathway (support-ing online text).To check which chemical groups of 3¶-terminal NMP participate in MgII stabilization and P2hydrolysis,we determined the cleavage reaction K d and k cat in MECs with RNAs containing chemical modifications in the phos-phate,sugar,and base of the 3¶-terminal nucleo-tide (Fig.2).The results (Table 1and table S1),discussed in detail in the supporting online text,are summarized below (see also fig.S3).With misincorporated adenosine 5¶-mono-phosphate,one of the P1oxygens interacts with the 3¶-hydroxyl,which in turn coordinates MgII.Another P1oxygen orients the active water molecule.The 2¶-hydroxyl does not participate in the reaction.N-7of the purine ring co-ordinates MgII;the amino group in position 6participates in water-molecule orientation or,alternatively,acts,together with nitrogen in position 1,as a general acid-base system.For misincorporated guanosine 5¶-monophosphate (GMP),one of the P1oxygens orients active water.The 2¶and 3¶hydroxyls do not participate in the reaction.N-7of the base coordinates MgII.The amino group in position 2fixes the GMP moiety,probably through interactions with the protein,making the reaction insensitive to local variations in nucleic acid structure.Table 1.K d for Mg 2þand k cat of P2cleavage for all possible CECs and MECs.All experiments were carried out in pH 7.9(40-C).K d and k cat values were calculated with the Michaelis-Menten equation.Complex 3¶-endNMP ofthe RNA Incorporated instead of K d (Mg 2þ)(mM)k cat(s j 1)CEC AA 100.004MECC 90.14G 80.12U 90.11CEC GG 90.001MECA 110.024C 150.028U 140.027CEC CC 570.001MECA 490.026G 150.029U 460.026CEC UU 370.001MECA 230.054C 80.015G300.043Fig. 2.Modifications of misincorporated 3¶-terminal nucleotides used in this study.A schematic representation of the active center of RNAP in MEC that is consistent with our findings is shown on the left.Structures of modified bases,phosphate groups,and sugars are shown.REPORTS SCIENCEVOL 31328JULY 2006519With misincorporated CMP,sequence de-pendence of the cleavage reaction in C-MECs is due to differences in the P1bond orientation,which appears to be sensitive to local variations of nucleic acids structure.In one type of complex,P1interacts with the 3¶-hydroxyl,which coordinates MgII.In other complexes,this interaction is absent,and the 3¶-hydroxyl does not chelate MgII.P1also participates in a network of hydrogen bonding that positions the active water molecule.The 2¶-hydroxyl is dispensable.Nitrogen in position 3of the base chelates MgII.Finally,with misincorporated UMP,P1interacts with the 3¶-hydroxyl,po-sitioning it to coordinate MgII or to orient the active water molecule.P1also participates in coordination of the active water molecule.The 2¶-hydroxyl is dispensable.The keto group in position 4of the base either positions the water molecule or acts in concert with N-3as a general base/acid.Taken together,the results indicate that nucleotides that are misincorporated at the transcript 3¶end participate in their own ex-cision.In contrast to the previously described stimulation of transcript cleavage by noncom-plementary NTP (4),which can be regarded as B substrate-assisted catalysis [(18,19),the reaction described here represents B product-assisted catalysis [and,therefore,can directly affect transcription fidelity.To show that excision of misincorporated NMP via P2cleavage can prevent transcription past misincorporated NMP,we supplied MECs with NTP specified by the þ2register of the template and monitored transcript extension (Fig.3).As noted for RNAPs from eukaryotes and archaea (10,17,20,21),the rate of incorporation of NTPs by MECs was much lower than by CECs (7,22)and was compara-ble (k obs ,0.03s j 1in the presence of 1mM NTP)to the rate of P2cleavage (Table 1).Presumably,slow elongation of misincorpo-rated transcripts is due to stabilization of MECs in a backtracked state and to the occupancy of the primary NTP binding site,the E-site,by misincorporated NMP.At 100m M NTP,only 5to 13%of MECs (30%for G-MEC)extended the RNA,whereas the rest of RNA was cleaved and,therefore,the misincorporated NMP was removed (Fig.3B).In the presence of 1mM NTP (a physiological concentration),È30%of complexes (50%for G-MEC)extended past incorrect NMP,whereas the remainder underwent cleavage (Fig.3B).When NTP was added together with transcript cleavage factor GreA,very low (except 20%for G-MEC)incorporation was detected,and mismatched NMP was removed (Fig.3B).Thus,cleavage stimulated by misincorporated nucleotides is sufficient to proofread most misincorpora-tion events.This activity is stimulated by transcript cleavage factors that were previ-ously suggested to contribute to transcrip-tional fidelity (10,12,17,21)and that act by direct stabilization of MgII in the RNAP ac-tive site (23).The importance of transcriptional proof-reading for error-free gene expression was suggested (24).In addition,complexes con-taining misincorporated nucleotides elongate RNA slowly,which should impede expression of actively transcribed genes and may interfere with DNA replication.Cleavage factors cannot be solely responsible for removal of misin-corporated nucleotides,because they are not essential for cells.Our results reveal a proof-reading mechanism that may be sufficient to control transcription misincorporation in theabsence of cleavage factors.The mechanism,which is likely evolutionarily conserved,also allows the removal of 2¶-deoxy NMPs erro-neously incorporated in RNA,because ribo and 2¶-deoxy NMPs cleaved out with the same efficiency.In the RNA-protein world,when RNAP was likely replicating RNA genomes (25),the rela-tively low fidelity of RNAP-catalyzed synthesis could not have been sufficient for stable maintenance of large RNA genomes in the absence of cleavage factors (24).A proofreading and repair mechanism similar to the one de-scribed here could have allowed a large RNA genome of the last common universal ancestor to exist.References and Notes1.T.A.Steitz,Nature 391,231(1998).2.P.Cramer,D.A.Bushnell,R.D.Kornberg,Science 292,1863(2001).3. D.G.Vassylyev et al.,Nature 417,712(2002).4.V.Sosunov et al.,EMBO J.22,2234(2003).5.K.D.Westover,D.A.Bushnell,R.D.Kornberg,Cell 119,481(2004).6.H.Kettenberger,K.J.Armache,P.Cramer,Mol.Cell 16,955(2004).7. D.Temiakov et al.,Mol.Cell 19,655(2005).8.T.A.Steitz,J.A.Steitz,Proc.Natl.Acad.Sci.U.S.A.90,6498(1993).9.M.Orlova,J.Newlands,A.Das,A.Goldfarb,S.Borukhov,Proc.Natl.Acad.Sci.U.S.A.92,4596(1995).10.M.J.Thomas,A.A.Platas,D.K.Hawley,Cell 93,627(1998).11.G.Bar-Nahum et al.,Cell 120,183(2005).12. D.A.Erie,O.Hajiseyedjavadi,M.C.Young,P.H.vonHippel,Science 262,867(1993).13.Materials and methods are available as supportingmaterial on Science Online.14.H.Guo,D.H.Price,J.Biol.Chem.268,18762(1993).15.M.G.Izban,D.S.Luse,J.Biol.Chem.268,12864(1993).16.S.K.Whitehall,C.Bardeleben,G.A.Kassavetis,J.Biol.Chem.269,2299(1994).nge,W.Hausner,Mol.Microbiol.52,1133(2004).18.P.Carter,J.A.Wells,Science 237,394(1987).19.W.Dall’Acqua,P.Carter,Protein Sci.9,1(2000).20.H.Matsuzaki,G.A.Kassavetis,E.P.Geiduschek,J.Mol.Biol.235,1173(1994).21. C.Jeon,K.Agarwal,Proc.Natl.Acad.Sci.U.S.A.93,13677(1996).22.J.E.Foster,S.F.Holmes,D.A.Erie,Cell 106,243(2001).ptenko,J.Lee,I.Lomakin,S.Borukhov,EMBO J.22,6322(2003).24. A.M.Poole,D.T.Logan,Mol.Biol.Evol.22,1444(2005).25. zcano,J.Fastag,P.Gariglio,C.Ramirez,J.Oro,J.Mol.Evol.27,365(1988).26.This work is dedicated to the memory of Dmitry Salonin.We thank E.P.Geiduschek for fruitful discussions.This work was supported by NIH grant RO1GM64530and a Burroughs Wellcome Career Award (to K.S.).Supporting Online Material/cgi/content/full/313/5786/518/DC1Materials and Methods SOM Text Figs.S1to S3Table S1References14March 2006;accepted 8June 200610.1126/science.1127422Fig.3.P2cleavage and transcriptional proofread-ing.(A )CECs and MECs [C-CEC (lanes 1and 2)and C(G)MEC (lanes 3to 12)are shown as exam-ples]were supplied with 15mM Mg 2þat pH 7.9(40-C)and incubated for various times with or without different concen-trations of CTP ,specified by the þ2register of template DNA and 1m M GreA.(B )Plots represent the relative amounts of MECs [A(U)MEC,C(G)MEC,G(C)MEC,and U(A)MEC are shown as examples]that incorporated NMP specified by the þ2reg-ister (white bars)and those that underwent P2cleavage (black bars)in an experiment similar to that shown in(A).REPORTS28JULY 2006VOL 313SCIENCE 520。

主题：transcription在生物学中的重要意义概述：1. transcription是生物学中的一个重要过程，是DNA转录成RNA 的过程。

2. transcription是生命活动的基本过程之一，对维持生物体内稳态具有重要意义。

意义：3. transcription是基因表达的第一步，决定了RNA的合成。

4. mRNA通过transcription合成后，能够传递DNA中的遗传信息，参与蛋白质的合成。

5. transcription在生物体内控制和调节基因表达，决定了细胞的功能和特性。

6. transcription在细胞分化、发育、免疫应答等生物学过程中起着至关重要的作用。

7. transcription异常可能导致疾病的发生，如肿瘤等。

具体过程：8. transcription包括启动、延伸、终止三个阶段，具体由RNA聚合酶和转录因子等调节蛋白参与。

9. 转录过程受到DNA序列、染色质构象和表观遗传学等多种因素的调控。

意义的举例说明：10. 在细胞分化过程中，不同细胞类型通过调控特定基因的转录，实现了细胞多样性和组织器官的形成。

11. 免疫细胞通过调节特定基因的转录，实现了在病原体感染或其他压力下的免疫应答。

应用前景：12. 针对转录过程的调控可用于基因治疗、细胞再生和疾病治疗等领域。

13. 利用转录调控技术可以实现特定基因的高效表达或沉默，为生物学研究和药物开发提供新的途径。

总结：14. transcription在生物学中的意义不可低估，对生命活动具有重要影响，其研究和应用前景广阔。

15. 深入理解转录过程的调控机制，有助于揭示生命活动的奥秘，推动生物医学领域的发展。

16. 进一步探究转录在生物学中的重要意义，可以看到它在遗传学、分子生物学和医学等领域具有广泛的应用。

通过观察转录过程，我们可以更好地理解基因调控的机制。

研究转录还有助于揭示疾病发生的分子机制，为新药研发提供理论基础。