RNA synthesis: 5’ → 3’
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Proofreading / 校正
U Remove U Add C C
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3. Termination / 终止
Intrinsic termination 内在型终止 ρ-dependent termination ρ依赖型终止
−10 box and −35 box
Transcription start site
5’
5’
3’
3’
-35 box+1-10 boxCoding region
Promoter
CCAGGCTTTACACTT - - -CGTATGTTGTGTGGAATT CTTTTTGATGCAATT - - -ACTATAATAGACAGGGTA GGCGGTGTTGACATA - - -GTGATACTGAGCACATCA
Region 1
Region 2
Region 3
Region 4
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The leader-attenuator RNA
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The coupled transcription-translation 偶联转录-翻译作用
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When tryptophan level is low …
半乳糖
葡萄糖
E. coli: “This is my favorite!”
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How to use lactose / 如何利用乳糖
E. coli: “I need lactose permease, β-galactosidase, and transacetylase.”
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lacA
CH2OH
OH
O
OH
O
CH2OH O OH
OH
OH
Lactose
OH
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1. Negative Regulation – High Trp level
High tryptophan level: No transcription
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Negative Regulation – low Trp level
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Lactose – the inducer Tryptophan – the co-repressor
(b) High tryptophan : transcription is repressed.
RNA polymerase cannot bind to the promoter
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Regulated 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
Lactose
Inducer 诱导物
Promoter Operator Leader -attenuator trpE
trpD
Aporepressor dimer
Repressor dimer
Co-repressor 辅阻遏物
Tryptophan
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The Trp Operon: No positive regulation
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2. Negative Regulation – the lac Repressor 负调控──lac阻遏蛋白
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Negative Regulation – the lac Repressor 负调控──lac阻遏蛋白
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3. Positive Regulation – CAP 正调控──CAP
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2. Attenuation / 衰减作用
Attenuator: “STOP!”
Not all transcription is repressed.
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The leader-attenuator region 前导子-衰减子区域
Promoter Operator Leader-attenuator trpE trpD trpC trpB trpA
Low tryptophan level: Transcription occurs
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lac repressor vs. trp repressor
Repressor
Low lactose level
(b) High tryptophan : transcription is repressed.
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Catalytic area of RNA polymerase
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3.2.3 Transcription Mechanism 3.2.3 转录机理
1. Initiation / 起始 2. Elongation / 延伸 3. Termination / 终止
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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
-35 box
-10 box
+1
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3.2.2 RNA Polymerase / RNA聚合酶
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Core enzyme vs. Holoenzyme
Holoenzyme starts transcription at promoters
Core enzyme starts transcription at random
Protein 3
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3.3.2 The lac Operon / 乳糖操纵子
Promoter Operator lacZ lacY lacA
The lac operon
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1. The Conditions of lactose Metabolism 1. 乳糖代谢的条件
乳糖
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When tryptophan level is high …
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3.3.4 Ara and Gal Operons 3.3.4 阿拉伯糖操纵子与半乳糖操纵子
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
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Regulation of gene expression 基因表达调控
Condition A
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Regulation of gene expression 基因表达调控
Chapter 3 / 第3章
Chapter 3 Transcription in Prokaryotes: Mechanism and Regulation 3.1 Why Use an RNA Intermediate?
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 Mechanism of Transcription 3.3 Regulation of Gene Expression
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Intrinsic termination / 内在型终止
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Base pair / 碱基对
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-dependent termination / 依赖型终止
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Rho proteins
X-Ray Crystal Structure Of Rho protein [MMDB ID:24381] 24 / 68
trpD trpC trpB trpA
CH
CH N H
COO – +H3N C H
CH3
Tryptophan
COO –
+H3N C H
CH2
C
CH N H
Promoter Operator lacZ
CH2OH
OH
O OH
OH
+
OH
Galactose
CH2OH O OH
OH OH
OH
Glucose
lacY
When to use lactose / 何时利用乳糖
Glucose + Lactose +
Glucose – Lactose –
Glucose – Lactose +
E. coli: “I will use lactose only when there is no glucose and there is lactose.”
in Prokaryotes 3.4 Experiments
3.2 转录机理 3.3 原核生物基因
表达调控 3.4 实验研究
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3.1 Why Use an RNA intermediate? 3.1 为什么使用RNA作为中间物？
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Chromosomes are large and complex
-35 box
-10 box
+1
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Consensus sequence / 共有序列
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。）