I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 A 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
10+1+10+20+30+40 Startpoint Promoter proximal distal Terminator Upstream<>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 As the bubble progresses, Polymerase moves dNA du uplex reforms behind it, displacing the 入A RNA in the form of a single polynucleotide chain 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 poin winding point 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
trinsic 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 CG C G G-C-nich region in stem C G C G
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 a, 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 rpoB阝 subunit (155kD) roc阝 subunit catalytic center (160kD) rpoD o subunit (3290kD) promoter specificity 入入 E. coli enzyme 465kD
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 sequences. (Numbers in the name ofa factor indicate its mass) Ge ene Factor Use -35 Sequence Separation 10 Sequence D 70 general TTGACA 16-18bp TATAAT rpo heat shock CCCTTGAA 13-15bp CCCGATNT rpoE heat shock not known not known not known rpoN nitrogen CTGGNA 6 b TTGCA fliA flagellar CTAAA 15b 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. 2.3N-terminus 200 0 600 is required for melting and 2.4 and 4.2 contact the -10 1.11.2 2.124 4.14.2 and -35 promotor Interactions with promoter elements. The N-terminal region prevents 2.4 and 4.2 pRevents DNA-binding from binding to DNA in the -10 35 bsence of core enzyme TAATAT ACAGTT 5
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 sequenc ↓↓↓↓↓↓↓↓ ↓↓↓ ↓↓↓ I Modification prevents XXXTTGACA Nontemplate strand RNA polymerase binding 4:李李 Unwinding ↑ RNA polymerase XXXXXX AACTG T XXXXXXXXXXXXXXXXXATA Template strand X XXXXXX protects against mod ification TTAXXXXXXX CX Mutations abolish or reduce promoter activity oints of contact lie on one face of DNA (on the nontemplate strand) 八 MN
One face of the promoter contains the contact points for RNA
