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Lecture 27 - Trnascription Termination - BIOL308.pdf

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BIOL 308
Bruce Wolff

Lecture 27Transcription TerminationAttenuation and TerminationRepressor is not the only control mechanismAttenuationregulated premature termination of transcriptionDoes not involve RhoPremature termination by attentuation at specific site attenuator site DNA sequence where RNA polymerase either terminates or continues with transcription different from normal termination site t siteSeveral operons use this type of control uncluding tryptophan phylalanine histidineReview negative regulation of trp operon by TrpRAnalysis of Ecoli Trp mutants which have high level of Trpsynthesizing enzymes even when repressed as Trp is high it binds to aporepressorFormed repressor binds to the operator which should stop transcription and consequently trp production but Shows that they haveNormal Trp repressorNormal Trp operatorNormal promoterBut there is deletion of 50 nucleotidesfrom the region that comes after promoteroperator but before coding sequence for Trp enzymesRegion total 162 nucleotides leader sequence L 140ntCodes for polypeptide which contains a few tryptophan amino acidsNecessary part of the leader sequence is 140nt long contains attenuator point of choice between elongation and terminationTrp abundantonly leader transcribedTrp lowin up to 50 cases RNAp passes attenuatorWhole RNA gets transcripedLeader sequence gets transcribedBalance between leader and total mRNA synthesis is in accordance with the need for trpFine tuningLeader Sequence NOTES FROM LECTURES Page 1
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