26 feb 2010 molbio

26 feb 2010 molbio - Mol bio lecture notes 26 February 2010...

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Mol bio lecture notes 26 February 2010 Bacterial Promoters All bacterial promoters have a conserved regulatory sequence called the -10 element Some bacterial promoters have an additional conserved sequence called the -35 element, others have a UP element and still others may have an extended -10 site. These extra sequences may be found in any combination. In general the strength of a promoter (level of gene expression) is correlated with the number of regulatory elements within the promoter. The numbers denote the position of the first base of each element relative to the transcription start site In bacteria these regulatory elements are bound by proteins called sigma factors. These proteins bind to the promoter and recruit RNA polymerase to DNA The first amino acid to be coded in every protein is methionine. TAC in DNA, AUG in mRNA. Sigma factors and the initiation of transcription Sigma factors are modular proteins and can bind several regulatory sequences at the same time Multiple sigma factors are bound to RNA polymerase while simultaneously being bound to the regulatory regions of the bacterial promoters. Thus, the sigma factors serve as a “bridging molecules” RNA polymerase is brought into close contact to the +1 site. Transcription begins at this site (also called TSS or transcriptional start site.) After the initiation phase is completed, the RNA polymerase reads and transcribes the DNA template (this is the elongation phase)
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