BIOL308 Lecture Notes - Tryptophan, Operon, Repressor
16 Jul 2014
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Premature 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 site) Several operons use this type of control, uncluding tryptophan, phylalanine, histidine . Review: negative regulation of trp operon by trpr. Analysis of e. coli trp mutants which have high level of trp synthesizing enzymes even when repressed as trp is high, it binds to aporepressor. Formed repressor binds to the operator which should stop transcription, and consequently trp production, but . But there is deletion of <50 nucleotides from the region that comes after promoter-operator but before coding sequence for. Region: total 162 nucleotides: leader sequence (l), 140nt. Codes for polypeptide which contains a few tryptophan amino acids. Necessary part of the leader sequence is 140nt long contains attenuator: point of choice between elongation and termination. Trp low: in up to 50% cases rnap passes attenuator.
