Spring 09 lecture 26

Spring 09 lecture 26 - RNA processing &...

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11 RNA processing & post-transcriptional control Learning Objectives Identify the requirements for rho-dependent and rho-independent transcription termination of E. coli RNAP Explain the mechanism of attenuation for the trp operon Termination of Prokaryotic and Eukaryotic Transcripts
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22 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
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33 about ½ of E. coli terminators require rho (ρ - stands for “release”) RN A rho is hexameric RNA helicase has RNA-binding domain (N-term) and 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. 11.33) Rho-dependent Termination
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44 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
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55 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.
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66 Attenuation and Termination
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77 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-
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This note was uploaded on 08/03/2009 for the course BIOL BIOL308 taught by Professor Miskovic during the Spring '09 term at Waterloo.

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Spring 09 lecture 26 - RNA processing &...

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