K 原核生物的转录.ppt

SECTION K Section K 原核生物的转录 K1 转录的基本原则 K2 Escherichia coli RNA 聚合酶 K3 The E. coli s70 promoter K4 转录的起始、延伸与终止 Transcription 是指以a double-stranded DNA 为模板合成 a single-stranded RNA . RNA synthesis occurs in the 5’3’direction and its sequence corresponds to that of the DNA strand which is known as the sense strand（有义链）.The template of RNA synthesis is the antisense strand. Necessary components: promoter/template, RNA polymerase, NTPs, terminator/template (-) strand is antisense strand. (+) strand is sense strand K1 转录的基本原则 Initiation: polymerase and promoters Elongation: RNA polymerase Termination: terminator ATACG TATGC +1 promoter terminator Transcribed region RNA DNA Transcription Antisense strand AUACG Structure of a transcription unit What is a promoter (启动子)? The sequence of DNA needed for RNA polymerase to bind to the template and accomplish the initiation reaction 位于蛋白质编码区的上游（5’端） 含有短而保守的DNA序列，不同基因的启动子中序列经常是保守的。 Initiation Binding of an RNA polymerase to the dsDNA（非专一不稳定的复合物在模板移动） Slide to find the promoter（封闭的“酶-启动子”二元复合物） Unwind the DNA helix （开放的“酶-启动子”二元复合物） Synthesis of the RNA strand at the start site (initiation site), this position called position +1 （“酶-启动子-rNTP”三元复合物） Transcription bubble Elongation RNA polymerase adds 核糖核苷酸 to the 3’-end and 延伸 the growing RNA chain in the direction of 5’ 3’ （E. coli: 40 nt/sec) 酶自身沿着反义DNA链（模板）的3’5’方向移动。 酶移动时局部解旋，经过后重新形成双螺旋。 Elongation Termination 转录复合物的解体 and separation of RNA strand from DNA Occurring at the terminator (often 茎环或发夹二级 structure), some need rho protein as accessory factor. RNA hairpin (发卡) structure 5‘ NNNNAAGCGCCGNNNNCCGGCGCUUUUUU -OH N N N N C G•C C•G C•G G•C C•G G•C A•U A•U … NNNN UUUU-OH Steps for RNA transcription 2. Requires DNA for activity and is most active with a double-stranded DNA as template. 5’  3’ synthesis (NMP)n + NTP  (NMP)n+1 + PPi RNA polymerase: synthesis of RNA strand from DNA template. 1. Requires no primer for polymerization 3. Require