K原核生物的转录学习教案

1、会计学1K原核原核(yun h)生物的转录生物的转录第一页，共55页。第1页/共54页第二页，共55页。第2页/共54页第三页，共55页。(-) strand is antisense strand. (+) strand is sense strand第3页/共54页第四页，共55页。第4页/共54页第五页，共55页。ATACGTATGC+1promoterterminatorTranscribed regionRNADNATranscriptionAntisense strandAUACGStructure of a transcription unit第5页/共54页第六页，共55页。W

2、hat 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(xli)，不同基因的启动子中序列(xli)经常是保守的。第6页/共54页第七页，共55页。第7页/共54页第八页，共55页。Transcription bubble第8页/共54页第九页，共55页。第9页/共54页第十页，共55页。Elongation第10页/共54页第十一页

3、，共55页。第11页/共54页第十二页，共55页。RNA hairpin (发卡(f k) structure5 NNNNAAGCGCCGNNNNCCGGCGCUUUUUU -OHNN NN CGCCGCGGCCGGCAUAU NNNN UUUU-OH第12页/共54页第十三页，共55页。Steps for RNA transcription第13页/共54页第十四页，共55页。2. Requires DNA for activity and is most active with a double-stranded DNA as template. 5 3 synthesis(NMP)n +

4、 NTP (NMP)n+1 + PPiRNA polymerase: synthesis of RNA strand from DNA template.1. Requires no primer for polymerization3. Require Mg2+ for RNA synthesis activity第14页/共54页第十五页，共55页。4. All RNA polymerases lack 3 5 exonuclease activity, and one error usually occurs when 104 to 105 nucleotides are incorpo

5、rated. 5. usually are multisubunit enzyme, but not always. 6. Different from organism to organism7. E. coli has a single DNA-directed RNA polymerase that synthesizes all types of RNA. 第15页/共54页第十六页，共55页。Both 起始(q sh) & 延伸起始(q sh) only36.5 KD36.5 KD151 KD155 KD11 KD70 KD465kd第16页/共54页第十七页，共55页。 R

6、NA synthesis rate: 40 nt per second at 37oC 非球形结构(jigu)，圆柱形孔道旁有一突起，孔道大小表明the enzyme complex can bind directly to 16 bp of DNA. The whole polymerase binds over 60 bp.第17页/共54页第十八页，共55页。E. coli RNA polymerase:全酶: 2 for initiation核心(hxn)酶: 2 for elongation第18页/共54页第十九页，共55页。RNA pol 亚基第19页/共54页第二十页，共55页

7、。第20页/共54页第二十一页，共55页。E. coli polymerase: b subunit 第21页/共54页第二十二页，共55页。（与模板结合（与模板结合(jih)有关）有关）.E. coli polymerase: b subunit 第22页/共54页第二十三页，共55页。E. coli polymerase: s factor 第23页/共54页第二十四页，共55页。RNA polRNA pol（30%30%）. . E. coli polymerase: s factor 第24页/共54页第二十五页，共55页。K3 The E. coli 70 promoter Prom

8、oter sequences: -10 sequence and -35 sequence2. Transcription start site3. Promoter efficiency第25页/共54页第二十六页，共55页。ATACGTATGC+1promoterterminatorTranscribed regionRNADNATranscriptionAntisense strandDifferent promoters result in differing efficiencies of transcription initiation, which in turn regulat

9、e transcription. AUACG第26页/共54页第二十七页，共55页。第27页/共54页第二十八页，共55页。第28页/共54页第二十九页，共55页。important for promoter function-5-8 bp- GC T ATTGACATATAAT-16-18 bp-+1-35 sequence-10 sequence第29页/共54页第三十页，共55页。n-10序列似乎是聚合酶启动序列似乎是聚合酶启动DNA解旋的序列解旋的序列第30页/共54页第三十一页，共55页。promoters第31页/共54页第三十二页，共55页。 A purine in 90% of

10、 all genes G is more common at position +1 than A Often, 起始(q sh)位点两侧为C and T (i.e. CGT or CAT)The sequence around the start site influences initiation第32页/共54页第三十三页，共55页。The sequences of five E. coli promotersConsensusTTGACATATAAT第33页/共54页第三十四页，共55页。promoter strength .第34页/共54页第三十五页，共55页。第35页/共54页第

11、三十六页，共55页。DNA unwinding RNA chain initiation RNA chain elongation RNA chain termination Rho-dependent termination 第36页/共54页第三十七页，共55页。Binding第37页/共54页第三十八页，共55页。UnwindingInitiationElongationTermination第38页/共54页第三十九页，共55页。第39页/共54页第四十页，共55页。polymerase and this process is referred to as tight binding

12、第40页/共54页第四十一页，共55页。聚合酶起始新一轮转录聚合酶起始新一轮转录(zhun l)重要作用重要作用nThe minimum time for promoter clearance is 1-2 seconds (a relatively long event)第41页/共54页第四十二页，共55页。第42页/共54页第四十三页，共55页。第43页/共54页第四十四页，共55页。antisense第44页/共54页第四十五页，共55页。第45页/共54页第四十六页，共55页。RNA chain 终止(zhngzh)Termination: dissociation of RNA r

13、e-annealing of DNA release of RNA polTerminator sequence 终止序列 (stop signal 停止(tngzh)信号): RNA hairpin very commonAccessory rho protein第46页/共54页第四十七页，共55页。第47页/共54页第四十八页，共55页。A model for -independent termination of transcription in E. coli. The A-U base-pairing is less stable that favors the dissociat

14、ion第48页/共54页第四十九页，共55页。2. Rho-dependent Termination. lNo U stretch at the 3 end of the RNAlRho protein (hexameric protein) binds to certain RNA structure (72bp) moves along the nascent RNA toward RNA pol complex stop at the rho-dependent transcription terminator. 第49页/共54页第五十页，共55页。第50页/共54页第五十一页，共5

15、5页。第51页/共54页第五十二页，共55页。RNA polDNA polTemplatedsDNA is betterss/dsDNARequire primerNoYesInitiationpromoteroriginelongation40 nt/ sec900 bp/secterminatorSynthesized RNA Template DNA第52页/共54页第五十三页，共55页。Summary:General features of RNA pol.E. coli RNA pol: holoenzyme (2b bs) and core enzyme (2b b). Role of sigma factor.E. coli s70 promoter: -35 sequence (TTGACA), -10 (TATAAT), & +1 (purine, G A)1. Transcripti