Chapter 5 transcription 分子生物学双语课程PPT

2 40×103
multiple
β rpoB β’ rpoC σ rpoD
1 155×10 Core catalytic 3 enzyme
1 160×10
catalytic
3
1 32×103 σ factor recognitio
~
n
Core enzyme
4 subunits: α2ββ' bind to DNA catalyze RNA synthesis but has no specificity.
TTGACA（Sextama Box）
17bp
-10 site：RNA pol. firmly binding site（B site） TATAAT（Pribnow Box）
7 bp
Initiation site ：+1 site RNA transcriptional startpoint （I site）
TTTACA -- 18 -- TATAAT TTTACA -- 18 -- TATGTT TTGACA -- 17 -- TATAAT
λ PRM Up-1
TAGACA -- 17 -- TAGATT
λ PRM wild-type TAGATA -- 17 -- TAGATT
TTGACA -- 17 -- TATAAT
5.1.2.1 The startpoint Promoter: a region of DNA where RNA polymerase binds to initiate transcription
原核生物启动子结构图

consensus sequence
core promoter
-35 site：RNA pol. loosely binding site （R site）
Chapter 5 RNA transcription
Central Dogma
Contents 1 The transcription in prokaryotes
2 The transcription in eukaryotes
3
RNA processing
4 Ribozyme 5 Reverse transcription
Holoenzyme
5 subunits: α2ββ'σ σ reduces the affinity of RNA polymerase for non-specific DNA and greatly increases its affinity for promoter
σ factor
Reusable； Change RNA pol conformation Recognize promoter Have no catalytic ability
Basic concepts
Transcription unit: a sequence of DNA transcribed into a single RNA, starting at the promoter and ending at the terminator. Transcript bubble Promoter: a region of DNA where RNA polymerase binds to initiate transcription Terminator: a sequence of DNA that causes RNA polymerase to terminate
(1960)
does not require a primer does not have the proofreading function does not initiate RNA synthesis randomly initiates synthesis at promoters
5.1.2 The mechanism of transcription
A/G
-35 (R)
-10 (B)
+1 (I) RNA
Promoter efficiency can be increased or decreased by mutation
up promoter mutations look more like the consensus
lac UV5 lac wild-type
Upstream Startsite (Startpoint) Downstream
5.1 The transcription in
prokaryotes
5.1.1 RNA polymerase
E. coli
Sub Codin No.
unit
g
gene
MW Position Function
α rpoA
5.1.2.2 The initiation of prokaryotic
transcription
RNA polymerase binds to one face of DNA to find promoter
转录起始复合物 转录泡上的三元复合物
5.1.2.3 Elongation
RNA pol moves along the template，then RNA elongation，and keep the triplex； In transcript bubble, DNA helix open, and then close， RNA elongation; As the bubble progresses, the DNA duplex reforms behind it, displacing the RNA in the form of a single polynucleotide chain. RNA elongation rate is constant, and it will slow down in GC-rich region. Transcription generates positive supercoils and negative supercoils.
down promoter mutations look less like the consensus
-10 Box was 17bp to -35 Box, it is easy to initiate for RNA pol
Close to 17 bp，up mutation Far from 17 bp，down mutation 17bp distance is more important to transcription than the sequence
Prokaryotes have the same core enzyme, but the σ factor is different.
E. coli RNA Polymerase function
Template: DNA Substrates: rNTPs Activator: Mg2+. Product: RNA