Biochemistry 2280A Lecture Notes - Catabolism, Chromatin, Conformational Change
7 Dec 2012
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Document Summary
There are 2 key reasons why some bacterial promoters are transcribed more than others: strength of the basic promoter elements not all -10 and -35 sequences are equally active. They bind rna polymerase holoenzyme with different affinities: more than one sigma factor. The most prevalent is the housekeeping sigma, 70. Others include 54 (nitrogen metabolism) and hs (heat shock: gene specific regulatory proteins bind specific dna sequences found in one or more promoters and serve to activate or repress transcription. Positive regulation factors activate transcription an activator protein (cap) regulates transcription of the lac operon and other genes involved in carbon metabolism. Negative regulation factors repress transcription - tryptophan (trp) repressor. In e. coli, the 5 genes (e, d, c, b, a) for tryptophan biosynthesis are transcribed as a single unit from a common promoter. The trp operon is expressed when there is a little tryptophan in the cellular environment.
