fall 09 lecture 26

fall 09 lecture 26 - Prokaryote Transcription Termination...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Prokaryote Transcription Termination Transcription termination better understood in prokaryotes Protein - coding regions are closely spaced in the prokaryotic genomes (little “junk” DNA) -Independent control - only if transcription termination site is between genes -Operons- coordinated control In E. coli transcription termination- 2 mechanisms: RNA polymerase only RNA polymerase + protein Rho Rho-dependent vs. Rho-independent termination Also: premature termination- attenuation
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 about ½ of E. coli terminators require rho (ρ - stands for “release”) RN A rho is hexameric RNA helicase has RNA-binding RNA-binding domain (N-term) and ATPase ATPase (C-term) activities binds to rut site (r ho ut ilization) on mRNA - rho has no affinity for RNAP tracks along RNA until it catches-up to RNAP RNAP pauses at termination site → provides time for catch-up (termination site often requires hairpin to be formed in secondary structure of RNA being transcribed) rho unwinds DNA-RNA hybrid (requires ATP) → mRNA, rho, RNAP all released (Lewin, 2006. Fig. 11.3 Rho-dependent Termination
Background image of page 2
3 Rho -Independent Termination Rho-independent termination site which have two characteristics: GC rich self- complementary region with several intervening nucleotides When this region is transcribed - forms stem loop structure Followed by series of U residues Experiments with mutants both loop forming sequences and U stretch are important
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Mutation analysis: Loop interacts with the “surface” of RNAP which just synthesized short polyU region This interaction causes RNAP to pause This U region at 3’ end of nascent RNA forms very weak bonds with complementary (template) A region Bonds melt during RNAP pause on the loop RNA chain is released DNA strands re-anneal RNAP dissociates from the DNA Rho -Independent Termination cont.
Background image of page 4
5 Attenuation and Termination Review: Negative regulation of trp Operon by TrpR
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 Attenuation and Termination Repressor- not the only control mechanism Attenuation - regulated premature termination of transcription Does not involve Rho Premature termination by attenuation at specific site- attenuator site - DNA sequence where RNA polymerase either terminates or continues with transcription - different from “normal” termination site (t site) Several operons, including phenylalanine, histidine…
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 23

fall 09 lecture 26 - Prokaryote Transcription Termination...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online