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