分子生物学张尚宏课件 分子生物学5.ppt

三、原核生物的基因转录及表达调控 1. 转录机器(装置)( transcription apparatus ) (1) RNA 聚合酶( RNA polymerase ) ??(40 kD ) ??(150 kD ), ?‘(160 kD ) ??(70 kD ): specificity factor ?核心酶( core enzyme ): ?,?‘,2 ??全酶( holoenzyme ): ?,?‘,2 ?, ??: specificity factor RNA polymerase ( holoenzyme ) 三、原核生物的基因转录及表达调控 1. 转录机器(装置)( transcription apparatus ) (2)启动子( promoter ) ?聚合酶的结合位点( binding site ), 一般位于转录起始位点上游? RNA 聚合酶与启动子的结合( RNA polymerase /promoter binding ) Closed plex Open plex ,转录才能开始 RNA polymerase / promoter binding (2)启动子( promoter ) ? Promoter structure 共同序列( consensus sequence ) ? Pribnow box (-10 box, David Pribnow 发现) ?-35 box ( -10 box 与-35 box 的最佳距离为 17 ? 1 bp ) ?下调突变( down mutation ) ?上调突变( up mutation ) Promoter structure ?下调突变( down mutation ) ?上调突变( up mutation ) (2)启动子( promoter ) ? Promoter structure 强启动子还有一些额外的元件,如 E. coli 编码 rRNA 的 rrn gene 中的 UP element (上游元件),可提高表达数十倍 Promoter structure (3)转录起始( transcription initiation ) Four steps: ? Formation of a closed plex ? Conversion of the closed promoter complex to an open plex ? Polymerizing the first few nucleotides (up to 10) while the polymerase remain at the promoter ? Promoter clearance