Biochemistry 2288A Lecture Notes - Lecture 21: Catabolite Activator Protein, Trp Operon, Lac Repressor

• School: Western University
• Department: Biochemistry
• Course: Biochemistry 2288A
• Professor: Chris Brandl

Document Summary

Regulation of gene expression: how are different bacterial promoters transcribed at different levels: some genes have better -10 and -35 sequences. If you have better -10 and -35 it means you have lots of polymerase there and lots of transcription. The (cid:373)ost pre(cid:448)ale(cid:374)t is the (cid:862)housekeepi(cid:374)g(cid:863) sig(cid:373)a (cid:894)sig(cid:373)a 70(cid:895) involved in the expression of most genes. Others include sigma 54-nitrogen metabolism, sigma 38-starvation, sigma hs-heat shock. Positive regulation-factors activate transcription (e. g. catabolite activator protein) Negative regulation-factors repress transcription (e. g. trp repressot, lac repressor) Rna polymerase from the promoter no transcription: when tryptophan concentration is low, tryptophan dissociates from the trp repressor the trp repressor no longer binds the trp operator rna pol binds the promoter transcription results. The recognition sequence is highly specific: tryptophan causes a conformational (shape) change in trp repressor that allows it to bind dna. Rna polymerase will access the promoter at all times if a mutation in the operator inhibits binding of the repressor.