1、1/68Chapter 3 /第第3章章Chapter 3Transcription in Prokaryotes:Mechanism and Regulation3.1 Why Use an RNA Intermediate?3.2 Mechanism of Transcription3.3 Regulation of Gene Expression in Prokaryotes3.4 Experiments第第3章章原核生物转录：原核生物转录：机理与调控机理与调控3.1 为什么使用为什么使用RNA 作为中间物？作为中间物？3.2 转录机理转录机理3.3 原核生物基因原核生物基因 表达调控表
2、达调控3.4 实验研究实验研究2/683.1 Why Use an RNA intermediate?3.1 为什么使用为什么使用RNA作为中间物？作为中间物？3/68Chromosomes are large and complexLow efficiency!DNAProteinRibosome4/68DNA must be stable5/68One mRNAmany proteins6/68More opportunities for regulationChapter 3Chapter 47/683.2 Mechanism of Transcription3.2 转录机理转录机理8/
3、683.2.1 Promoters/启动子启动子9/6810 box and 35 boxCCAGCCAGGCTTTACACGCTTTACACTT-CGTT-CGTATGTTGTATGTTGTGTGGTGTGGA AATTATTCTTTCTTTTTGATGCAATTGATGCAATT-ACTT-ACTATAATATATAATAGACAGGACAGG GGTAGTAGGCGGGCGGTGTTGACAGTGTTGACATA-GTTA-GTGATACTGGATACTGAGCACAGCACA ATCATCA -35 box -10 box +110/68Consensus sequence /共有序列
4、共有序列CCAGCCAGGCTTTACACGCTTTACACTT-CGTT-CGTATGTTGTATGTTGTGTGGTGTGGA AATTATTCTTTCTTTTTGATGCAATTGATGCAATT-ACTT-ACTATAATTATAATA AGACAGGACAGG GGTAGTAGGCGGGCGGTGGTGTTGACATTGACATA-GTTA-GTGATACTGGATACTGAGCACAGCACA ATCATCA -35 box -10 box +1TATAATTATAATTTGACATTGACAConsensus sequencesConsensus sequence:a gener
5、alized sequence from which most actual sequences differ very little or not at all.（共有序列共有序列：一种普遍的序列，：一种普遍的序列，大多数实际的序列与它相差很小或完全相同。）大多数实际的序列与它相差很小或完全相同。）11/683.2.2 RNA Polymerase /RNA聚合酶聚合酶12/68Core enzyme vs.HoloenzymeHoloenzyme starts transcription at promotersCore enzyme starts transcription at ran
6、dom13/68Catalytic area of RNA polymerase14/683.2.3 Transcription Mechanism3.2.3 转录机理转录机理1.Initiation /起始起始2.Elongation /延伸延伸3.Termination /终止终止15/681.Initiation /起始起始Step 1Step 216/68Initiation /起始起始Step 3Step 417/682.Elongation /延伸延伸Transcription bubble18/68The polymerization reaction聚合反应聚合反应RNA sy
7、nthesis:5 319/68Proofreading /校正校正UCRemove UAdd C20/683.Termination /终止终止Intrinsic termination内在型终止内在型终止-dependent termination依赖型终止依赖型终止 21/68Intrinsic termination /内在型终止内在型终止 22/68Base pair /碱基对碱基对23/68-dependent termination /依赖型终止依赖型终止 24/68Rho proteinsX-Ray Crystal Structure Of Rho protein MMDB I
8、D:24381 25/683.3 Regulation of gene expression in prokaryotes3.3 原核生物基因表达调控原核生物基因表达调控3.3.1 Coordinate Regulation3.3.2 The Lac Operon3.3.3 The Trp Operon3.3.4 Ara&Gal Operons3.3.1 协同调控协同调控3.3.2 乳糖操纵子乳糖操纵子3.3.3 色氨酸操纵子色氨酸操纵子3.3.4 阿拉伯糖与阿拉伯糖与 半乳糖操纵子半乳糖操纵子26/68Regulation of gene expression基因表达调控基因表达调控Cond
9、ition A27/68Regulation of gene expression基因表达调控基因表达调控Condition B28/683.3.1 Coordinate Regulation协同调控协同调控Operator操纵基因操纵基因operon29/68Polycistronic mRNA多顺反子多顺反子mRNAPolycistronic mRNATranslationProtein 1Protein 2Protein 330/683.3.2 The lac Operon /乳糖操纵子乳糖操纵子The lac operon31/681.The Conditions of lactose
10、 Metabolism1.乳糖代谢的条件乳糖代谢的条件E.coli:“This is my favorite!”乳糖乳糖半乳糖半乳糖葡萄糖葡萄糖32/68How to use lactose /如何利用乳糖如何利用乳糖E.coli:“I needlactose permease,-galactosidase,andtransacetylase.”33/68When to use lactose /何时利用乳糖何时利用乳糖E.coli:“I will use lactose only when there is no glucose and there is lactose.”Glucose+L
11、actose+Glucose Lactose Glucose Lactose+34/68Regulated Expression of Lactose Metabolizing Genes乳糖代谢基因表达调控乳糖代谢基因表达调控1.Negative Regulation the lac Repressor 负调控负调控lac阻遏蛋白阻遏蛋白2.Positive Regulation CAP 正调控正调控CAP35/682.Negative Regulation the lac Repressor负调控负调控lac阻遏蛋白阻遏蛋白36/68Negative Regulation the lac
12、Repressor负调控负调控lac阻遏蛋白阻遏蛋白37/683.Positive Regulation CAP 正调控正调控CAP38/68CAP-cAMP complexcAMPCAPDNACAPcAMP39/68Adenylyl Cyclase(AC)OOCH2AO POOOHcAMPATPACGlucose inhibits the activity of AC.40/68CAP “The accelerator”lac repressor “The brake”Brake刹车刹车Accelerator加速器加速器42/683.3.3 The Trp Operon /色氨酸操纵子色氨酸
13、操纵子NHCHCCH2CH+H3NCOO NHCHCHCH3CH+H3NCOO TryptophanOHOH43/681.Negative Regulation High Trp levelHigh tryptophan level:No transcription44/68Negative Regulation low Trp levelLow tryptophan level:Transcription occurs45/68lac repressor vs.trp repressorPromoter Leader-attenuator trpEtrpDAporepressordimerT
14、ryptophanRepressor dimerRNA polymerase cannot bind to the promoterOperator(b)High tryptophan:transcription is repressed.High tryptophan levelLowlactose level46/68Promoter Leader-attenuator trpEtrpDAporepressordimerTryptophanRepressor dimerRNA polymerase cannot bind to the promoterOperator(b)High try
15、ptophan:transcription is repressed.Lactose the inducer Tryptophan the co-repressorInducer 诱导物诱导物Co-repressor辅阻遏物辅阻遏物47/68The Trp Operon:No positive regulation48/682.Attenuation /衰减作用衰减作用Not all transcription is repressed.Attenuator:“STOP!”49/68The leader-attenuator region前导子前导子-衰减子区域衰减子区域50/68The le
16、ader-attenuator RNA51/68The coupled transcription-translation偶联转录偶联转录-翻译作用翻译作用52/68When tryptophan level is low 53/68When tryptophan level is high 54/683.3.4 Ara and Gal Operons 3.3.4 阿拉伯糖操纵子与半乳糖操纵子阿拉伯糖操纵子与半乳糖操纵子半乳糖半乳糖CHOHO C HH C OHH C OHCH2OHArabinose阿拉伯糖阿拉伯糖55/681.Ara Operon /阿拉伯糖操纵子阿拉伯糖操纵子When t
17、here is no arabinose,the operon is repressed.56/68Ara Operon /阿拉伯糖操纵子阿拉伯糖操纵子When there is arabinose,the operon is induced.57/682.Gal Operon /半乳糖操纵子半乳糖操纵子When there is no galactose,the operon is repressed.58/68Gal Operon /半乳糖操纵子半乳糖操纵子When there is galactose,the operon is induced.59/683.4 Experiments /实验研究实验研究The lac operon60/68Constitutive mutant lacI/组成型突变体组成型突变体lacIThe lost function was compensated.61/68Constitutive mutant lacOC/组成型突变体组成型突变体lacOCThe lost function was NOT compensated.62/68LacOc functions only on the same DNA fragment63/68Structure of the lac operon乳糖操纵子的结构乳糖操纵子的结构
