k原核生物的轉(zhuǎn)錄ppt課件-資料下載頁(yè)
2025-05-12 05:33本頁(yè)面
【正文】 個(gè)聚合酶起始新一輪轉(zhuǎn)錄重要作用 ? The minimum time for promoter clearance is 12 seconds (a relatively long event) RNA chain 延伸 ? σFactor is released to form a ternary plex of the polDNARNA (newly synthesized), causing the polymerase to progress along the DNA (promoter clearance) ? Transcription bubble (unwound DNA region, ~ 17 bp) moves along the DNA with RNA polymerase which unwinds DNA at the front and rewinds it at the rear ? 3’ part of RNA forms hybrid helix (ca. 12bp) with antisense DNA strand. ? The E. coli polymerase moves at an average rate of ~ 40 nt per sec, depending on the local DNA sequence. antisense RNA chain 終止 ? Termination: dissociation of RNA reannealing of DNA release of RNA pol ? Terminator sequence 終止序列 (stop signal 停止信號(hào) ): ? RNA hairpin very mon ? Accessory rho protein RNA hairpin 1. RNA 轉(zhuǎn)錄物是自身互補(bǔ)的 2. GCrich favouring the base pairing stability and causing the polymerase to pause 3. Followed by a stretch of four or more Us which result in weak RNAantisense DNA strand binding，有利于解離 A model for ρindependent termination of transcription in E. coli. The AU basepairing is less stable that favors the dissociation 2. Rhodependent Termination. ? No U stretch at the 3’ end of the RNA ? Rho protein (hexameric protein) binds to certain RNA structure (72bp) ? moves along the nascent RNA toward RNA pol plex ? stop at the rhodependent transcription terminator. 注意 ? 終止信號(hào)的識(shí)別發(fā)生在新合成的 RNA連而不是在模板 DNA鏈中。 RNA polymerase/transcription and DNA polymerase/replication RNA pol DNA pol Template dsDNA is better ss/dsDNA Require primer No Yes Initiation promoter origin elongation 40 nt/ sec 900 bp/sec terminator Synthesized RNA Template DNA Summary: 1. General features of RNA pol. 2. E. coli RNA pol: holoenzyme (?2? ?’?s) and core enzyme (?2? ?’?). Role of sigma factor. 3. E. coli s70 promoter: 35 sequence (TTGACA), 10 (TATAAT), amp。 +1 (purine, G A) 4. Transcription: initiation, elongation and termination (hairpin and rho factor)
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