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1、Chapter 3 / 第3章,Chapter 3 Transcription in Prokaryotes: Mechanism and Regulation 3.1 Why Use an RNA Intermediate? 3.2 Mechanism of Transcription 3.3 Regulation of Gene Expression in Prokaryotes 3.4 Experiments,第3章 原核生物转录： 机理与调控 3.1 为什么使用RNA 作为中间物？ 3.2 转录机理 3.3 原核生物基因 表达调控 3.4 实验研究,3.1 Why Use an RNA
2、 intermediate? 3.1 为什么使用RNA作为中间物？,Chromosomes are large and complex,Low efficiency !,DNA,Protein,Ribosome,DNA must be stablee,One mRNA many proteins,More opportunities for regulation,3.2 Mechanism of Transcription 3.2 转录机理,3.2.1 Promoters / 启动子,10 box and 35 box,CCAGGCTTTACACTT - - -CGTATGTTGTGTGGAA
3、TT CTTTTTGATGCAATT - - -ACTATAATAGACAGGGTA GGCGGTGTTGACATA - - -GTGATACTGAGCACATCA,-35 box -10 box +1,Consensus sequence / 共有序列,CCAGGCTTTACACTT - - -CGTATGTTGTGTGGAATT CTTTTTGATGCAATT - - -ACTATAATAGACAGGGTA GGCGGTGTTGACATA - - -GTGATACTGAGCACATCA,-35 box -10 box +1,TATAAT,TTGACA,Consensus sequences
4、,Consensus sequence: a generalized sequence from which most actual sequences differ very little or not at all. （共有序列：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。）,3.2.2 RNA Polymerase / RNA聚合酶,Core enzyme vs. Holoenzyme,Holoenzyme starts transcription at promoters,Core enzyme starts transcription at random,Catalyti
5、c area of RNA polymerase,3.2.3 Transcription Mechanism 3.2.3 转录机理,Initiation / 起始 Elongation / 延伸 Termination / 终止,1. Initiation / 起始,Initiation / 起始,2. Elongation / 延伸,The polymerization reaction 聚合反应,RNA synthesis: 5 3,Proofreading / 校正,Remove U,Add C,Now showing Transcription,File: biophoto7 Life
6、 Transcription. (5),3. Termination / 终止,Intrinsic termination 内在型终止 -dependent termination 依赖型终止,Intrinsic termination / 内在型终止,Base pair / 碱基对,-dependent termination / 依赖型终止,Rho proteins,X-Ray Crystal Structure Of Rho protein MMDB ID:24381,Now showing Bacterial Transcription,File: biophoto7 Genetics
7、: A Conceptual Approach Bacterial transcription (6).,3.3 Regulation of gene expression in prokaryotes 3.3 原核生物基因表达调控,3.3.1 Coordinate Regulation 3.3.2 The Lac Operon 3.3.3 The Trp Operon 3.3.4 Ara & Gal Operons,3.3.1 协同调控 3.3.2 乳糖操纵子 3.3.3 色氨酸操纵子 3.3.4 阿拉伯糖与 半乳糖操纵子,Regulation of gene expression 基因表达
8、调控,Condition A,Regulation of gene expression 基因表达调控,Condition B,3.3.1 Coordinate Regulation 协同调控,Polycistronic mRNA 多顺反子mRNA,Polycistronic mRNA,Translation,Protein 1,Protein 2,Protein 3,3.3.2 The lac Operon / 乳糖操纵子,The lac operon,1. The Conditions of lactose Metabolism 1. 乳糖代谢的条件,E. coli: “This is m
9、y favorite!”,乳糖,半乳糖,葡萄糖,How to use lactose / 如何利用乳糖,E. coli: “I need lactose permease, -galactosidase, and transacetylase.”,When to use lactose / 何时利用乳糖,E. coli: “I will use lactose only when there is no glucose and there is lactose.”,Glucose + Lactose +,Glucose Lactose ,Glucose Lactose +,Regulated
10、Expression of Lactose Metabolizing Genes 乳糖代谢基因表达调控,1. Negative Regulation the lac Repressor 负调控lac阻遏蛋白 2. Positive Regulation CAP 正调控CAP,2. Negative Regulation the lac Repressor负调控lac阻遏蛋白,Negative Regulation the lac Repressor 负调控lac阻遏蛋白,3. Positive Regulation CAP 正调控CAP,CAP-cAMP complex,cAMP,CAP,DN
11、A,CAP,cAMP,Adenylyl Cyclase (AC),cAMP,ATP,AC,Glucose inhibits the activity of AC.,CAP “The accelerator” lac repressor “The brake”,Brake 刹车,Accelerator 加速器,Now showing The lac operon,File: biophoto7 Genetics: A Conceptual Approach The lac operon (15),3.3.3 The Trp Operon / 色氨酸操纵子,Tryptophan,OH,OH,1.
12、Negative Regulation High Trp level,Negative Regulation low Trp level,lac repressor vs. trp repressor,Promoter Leader,-,attenuator,trpE,trpD,Aporepressor,dimer,Tryptophan,Repressor,dimer,RNA polymerase cannot,bind to the promoter,Operator,(b) High,tryptophan,: transcription is repressed.,High tryptop
13、han level,Low lactose level,Promoter Leader,-,attenuator,trpE,trpD,Aporepressor,dimer,Tryptophan,Repressor,dimer,RNA polymerase cannot,bind to the promoter,Operator,(b) High,tryptophan,: transcription is repressed.,Lactose the inducer Tryptophan the co-repressor,Inducer 诱导物,Co-repressor 辅阻遏物,Now sho
14、wing The trp operon,File: biophoto7 Life The trp operon (6),The Trp Operon: No positive regulation,2. Attenuation / 衰减作用,Not all transcription is repressed.,Attenuator: “STOP!”,The leader-attenuator region 前导子-衰减子区域,The leader-attenuator RNA,The coupled transcription-translation偶联转录-翻译作用,When trypto
15、phan level is low ,When tryptophan level is high ,Now showing Attenuation,File: biophoto7 Genetics: A Conceptual Approach Attenuation (10),3.3.4 Ara and Gal Operons 3.3.4 阿拉伯糖操纵子与半乳糖操纵子,半乳糖,Arabinose 阿拉伯糖,1. Ara Operon / 阿拉伯糖操纵子,Ara Operon / 阿拉伯糖操纵子,2. Gal Operon / 半乳糖操纵子,Gal Operon / 半乳糖操纵子,3.4 Experiments / 实验研究,The lac operon,Constitutive mutant lacI / 组成型突变体lacI,Constitutive mutant lacOC / 组成型突变体lacOC,LacOc functions only on the same
