第2讲转录、基因的表达与调控转录是以DNA为模板，在依赖于DNA的RNA(transcription)聚合酶的催化下，以四种rNTP(ATP、CTP、GTP、和UTP)为原料，合成RNA的过程DNA双链分子带有遗传信息的链一基因链gene strand)=有义链(sence strand)The coding strand (Sense strand) of DNA hasthe same sequence as the mRNA and is relatedby the genetic code to the protein sequencethat it represents
第2讲 转录、基因的表达与调控 转录（transcription）是以DNA为模板，在依赖于DNA的RNA 聚合酶的催化下，以四种rNTP(ATP、CTP、GTP、和UTP)为原 料，合成RNA的过程。 DNA双链分子 带有遗传信息的链→基因链（gene strand） =有义链（sence strand） The coding strand (Sense strand) of DNA has the same sequence as the mRNA and is related by the genetic code to the protein sequence that it represents
另一条与其互补的链一→反基因链（antigenestrand）=反义链The antisense strand (Template strand) ofDNA is complementary to the sensestrand, and is the one that acts as thetemplate for synthesis of mRNA.所有基因均以反基因链为模板进行互补转录因而转录产物的碱基顺序必与基因的遗传信息一致3DNA模板的方向为3'一5'，转录产物为5"真核细胞：rRNA在核仁内转录mRNA与tRNA在核质中转录
另一条与其互补的链→反基因链（antigene strand）=反义链 The antisense strand (Template strand) of DNA is complementary to the sense strand, and is the one that acts as the template for synthesis of mRNA. 所有基因均以反基因链为模板进行互补转录 因而转录产物的碱基顺序必与基因的遗传信息一致 DNA模板的方向为3’→5’，转录产物为5’→3’ 真核细胞： rRNA在核仁内转录 mRNA与tRNA在核质中转录
第一节转录酶和转录因子一、RNA聚合酶在原核生物中，一个RNA聚合酶转录所有的基因。转录延伸大肠杆菌RNA聚合酶核心酶=α2β因子十核心酶=全酶一→起始RNA的合成6因子的功能：识别启动子并将封闭的启动子复合物转换成开放的状态。一旦转录起始，因子从全酶中脱离。因子的基本功能是增加RNA聚合酶对启动子的特异性结合，减少非特异性结合。一个因子（E.co/i中是70）起始大部分基因的转录，而其他因子识别不同的启动子，可以诱导特殊基因的协同表达
第一节 转录酶和转录因子 一、RNA聚合酶 在原核生物中，一个RNA聚合酶转录所有的基因。 大肠杆菌RNA聚合酶 核心酶＝2’ 转录延伸 因子＋核心酶＝全酶→起始RNA的合成 因子的功能：识别启动子并将封闭的启动子复合物转换成开放的 状态。一旦转录起始， 因子从全酶中脱离。 因子的基本功能是 增加RNA聚合酶对启动子的特异性结合，减少非特异性结合。 一个因子（E.coli中是 70）起始大部分基因的转录，而其他 因子识别不同的启动子，可以诱导特殊基因的协同表达
核心酶= α2 β大肠杆菌RNA聚合酶RNApolvmerasehas4typesofsubunitFunctionsGeneproductenzymeassemblyBandβ'subunitscontactDNAandRNApromoterrecognitionrpoA 2αsubunitsbindssomeactivators(40kDeachβsubunitBsubunitrpoBUpstreamDownstream（155kD)DNAcatalyticcenterRNA5β'subunitrpoc(160kD)β'subunito subunitvirtualtextwww.ergito.comrpoD(32-90kD)promoterspecificityFigure9.17Boththe templateand coding strands of DNAarecontactedbytheβandβsubunitslargelyintheregionof thetranscription bubble and downstream.The RNA iscontactedE.coli enzymemostly in the transcription bubble,(Usually thereis noXXX=465kDdownstreamRNA,and contacts withRNAdownstreamoccuronlyin the special casewhen the enzyme backtracks.)(Based@virtualtext.www.ergito.comondataof1903.)Figure9.16EubacterialRNApolymerases havefour types of subunit:αβandβ have ratherconstant sizes in different bacterial species,but varies more widely
大肠杆菌RNA聚合酶 核心酶＝ 2 ’
Sigmafactor controls specificityCore enzymebinds to any DNAXVXXXX核心酶不加区别Sigma destabilizes bindingXXXX地与任何DNA结Sigma合，因子减少这种结合，与核心酶形成全酶与Holoenzymebindstopromoter特定的启动子结V合evirtualtextwww.ergito.comFigure 9.18 Core enzymebinds indiscriminately to anyDNASigma factor reduces the affinity for sequence-independentbinding,andconfersspecificityforpromoters
核心酶不加区别 地与任何DNA结 合，σ因子减少 这种结合，与核 心酶形成全酶与 特定的启动子结 合
RNA polymerase surrounds the bubbleEnzymemovementDNA coding strandRewinding pointUnwindingpointDNAtemplatestrandCatalytic siteRNA binding site@virtualtextwww.ergito.comFigure 9.5 During transcription,thebubble is maintained within bacterial RNApolymerase,which unwinds and rewindsDNA,maintains the conditions of thepartner and template DNA strands,andsynthesizes RNA
RNA polymerase has a channel forDNAβ subunitNontemplatestrandRNAtranscriptTemplatestrandβ'subunitwww.ergito.comFigure9.8Theβ(cyan)andβsubunit(pink)ofRNApolymerase have a channel for the DNA template.Synthesis ofan RNA transcript (copper)has just begun; the DNA template(red)andcoding(yellow)strandsareseparatedinatranscription bubble.Photograph kindlyprovided by SethDarst
Theactivesiteholds thetranscriptionbubbleEnzymeholds~10bpupstreamTranscriptionbubbleis~25bpRNA-DNAhybridhas9bpBases areEnzymeholdsflipped out-10bpdownstreamofDNAhelix@virtualtextwww.ergito.comFigure 9.13 An expanded view of the active site shows thesharpturn inthepathofDNA
Sigma controlspromoterrecognition原核生物一种RNAHoloenzymewith70recognizesonesetofpromoters聚合酶转录所有X的基因，其中因子控制启动子由于。的识别。因子替代引导核Substitutionofsigmafactoncausesenzymetorecognizea differentsetofpromoters心酶去识别一组X不同的启动子。X@virtualtext.www.ergito.conFigure 9.31The sigma factor associated with core enzymedeterminesthesetof promoters wheretranscriptionisinitiated
原核生物一种RNA 聚合酶转录所有 的基因 ，其中σ 因子控制启动子 的识别。 由于σ 因子替代引导核 心酶去识别一组 不同的启动子
E.colihasseveral sigmafactorsFactorUseGene070generalrpoDosE.coli有几rposstress32rpohheatshock种不同的因子GErpoEheatshock054rponnitrogen28-fliAflagellaroOevirtualtextwww.ergito.comFigure 9.32 In addition to 70, E.coli has several sigmafactors that are induced by particular cnvironmcntal conditions.(Anumberinthenameof afactorindicates its mass.)Sigmafactors recognizepromoters byconsensus sequencesGene不同的因Factor -35SequenceSeparation-10 Sequence070TATAATrpoDTTGACA16-18bp子识别不同O32CCCTTGAACCCGATNTrpoH13-15bpo54CTGGNATTGCArpon6bp启动子的保28FCTAAAfliA15bpGCCGATAAa()gHGCTGAATCAsigHAGGANPuPu11-12bp守序列virtualtext.www.ergito.comFigure 9.34E.coli sigmafactors recognize promoterswithdifferentconsensussequences
E. coli 有几 种不同的σ因子 不同的σ因 子识别不同 启动子的保 守序列