Ⅲl基因的转录
III、基因的转录
基因转录:DNA—mRNA Template strand Coding strand ATGCGCCATGCCAGTTACGTACATGGA TACGCGGTACGGTCAATGCATCTACCT RNA sequence is TRANSCRIPTION complementary to template strand identical to coding strand UACGCGGUACGGUCAAUGCAUCUACCU RNA transcript The function of polymerase is to copy one strand of duplex dNa into RNA
基因转录：DNA mRNA The function of polymerase is to copy one strand of duplex DNA into RNA
NAANAA 10+1+10+20+30+40 Startpoint Promoter proximal distal Terminator Downstream a transcription unit is a sequence of DNa transcribed into a single rna starting at the promoter and ending at the terminator
A transcription unit is a sequence of DNA transcribed into a single RNA ， starting at the promoter and ending at the terminator
Transcription bubble in RNA polymerase Otebuhe progresses, the Polymerase moves DNA duplex reforms behind it, displacing the RNA in the form of a single polynucleotide chain 入AO RNA chain grows longer
As the bubble progresses,the DNA duplex reforms behind it,displacing the RNA in the form of a single polynucleotide chain
During transcription, the bubble is maintained within bacterial RNa polymerase, which unwinds and rewinds DNA, maintains the conditions of the partner and template RNA Strands, and synthesizes rna Enzyme movement DNA coding strand Rewinding point Unwinding p DNA template strand Catalytic site RNA binding site
During transcription,the bubble is maintained within bacterial RNA polymerase,which unwinds and rewinds DNA,maintains the conditions of the partner and template RNA strands,and synthesizes RNA
Intrinsic terminators include palindromic regions that from hairpins varying in length from 7 to 20 op The stem-loop structure includes a G-C-rich b region and is followed by a run of U residues C G G C C G C G G-C-rich region in stem C G GC UUUUK Single-stranded U-run
Intrinsic terminators include palindromic regions that from hairpins varying in length from 7 to 20 bp.The stem-loop structure includes a G-C-rich region and is followed by a run of U residues
Yeast RNA polymerase has grooves that could be binding sites for nucleic acids. The pink beads show a possible path for DNA that is -25A wide and 5 10A deep. The green beads show a narrower channel, 12-15A wide and -20A deep, that could hold RNA Photograph kindly provided by roger Kornberg
Yeast RNA polymerase has grooves that could be binding sites for nucleic acids.The pink beads show a possible path for DNA that is ~25Å wide and 5- 10Å deep.The green beads show a narrower channel,12-15Å wide and ~20Å deep,that could hold RNA.Photograph kindly provided by Roger Kornberg
Eubacterial RNA polymerase have four types of subunit au,B, and B have rather constant sizes in different bacterial species, but o varies more widely Gene product Functions enzyme assembly rpoA 2 a subunits promoter recognition (40 kD each) binds some activators roB阝 subunit (155kD) rpoc B subunit catalytic center (160kD) rpoD o subunit 2-90kD) promoter specificity 入入 E coli enzyme 465 kD
Eubacterial RNA polymerase have four types of subunit; α,β,and β’ have rather constant sizes in different bacterial species,but σ varies more widely
E coli sigma factors recognize promoters with different consensus quences. Numbers in the name of a factor indicate its mass) Gene Factor Use -35 Sequence Separation 10 Sequence D 70 gener TTGACA 16-18b TATAAT rpoH heat shock CCCTTGAA 13-15 bp CCCGATNT rpoE heat shock not known not known not known rpoN nitrogen CTGGNA 6 bp TTGCA flagellar CTAAA 15 bp GCCGATAA A map of the E coli o70 factor Core enzyme identifies conserved binding Melting regions. Regions 2. 1 and 2.2 个个 contact core polymerase. 2. 3 N-terminus 200 600 is required for melting, and 2. 4 and 4.2 contact the-10 1.1 1.2 2.124 4.14.2 Interactions with promoter and-35 promotor elements The N-terminal Prevents DNA-binding region prevents 2. 4 and 4.2 from binding to dNa in the 10 TAATAT ACAGTT 5 absence of core enzyme
A map of the E.coli σ 70 factor identifies conserved regions.Regions 2.1 and 2.2 contact core polymerase,2.3 is required for melting,and 2.4 and 4.2 contact the -10 and -35 promotor elements.The N-terminal region prevents 2.4 and 4.2 from binding to DNA in the absence of core enzyme. E.colisigma factors recognize promoters with different consensus sequences.(Numbers in the name of a factor indicate its mass)
One face of the promoter contains the contact points for RNA -35 sequence -10 sequence ↓44↓↓ ↓↓↓↓↓ mOdification prevents contemplate stran RNA polymerase binding +t **t uNwinding f RNA polymerase XXXXXX AACTG T XXXXXXXXXXXXXXXXXAT Template strand XXXXX TTAXXXXXXX AX Mutations abolish or educe promoter actvty Most points of contact lie on one face of DNA (on the nontemplate strand)
One face of the promoter contains the contact points for RNA