Spring 09 lecture 17

Spring 09 lecture 17 - Various Sigma Subunits E. coli has...

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Unformatted text preview: Various Sigma Subunits E. coli has various sigma ( & ) subunits; h directs the holoenzyme to specific promoters - each different sigma factor recognizes a specific promoter sequence Specific gene expression fast transcription initiation under specific conditions: 70 recognizes promoters in most genes (constitutive transcription mostly) 32 promoters for genes induced by heat shock 28 promoters for genes for motility and chemotaxis 38 promoters for genes for stationary phase and stress response 54 promoters for genes for nitrogen metabolism and other factors E. coli RNAP promoters Promoters: sites that are critical for binding of RNAP Promoters are asymmetrical direct positioning of RNAP RNAP binds to dsDNA; nucleotide sequence that is on the coding strand (in 5-3 orientation) and precedes the coding sequence for the mRNA is usually given/written *Rememeber: consensus sequence(s) , in general, are the nucleotides most commonly found in a certain position in sequences of DNA or RNA of related function. Sclavi, Bianca et al. (2005) Proc. Natl. Acad. Sci. USA 102, 4706-4711 Promoter determines: 1.Which strand will serve as a template. 2.Transcription starting point. 3.Strength of polymerase binding. FYI: Some promoters lack 35 region but they have extended 10 region Promoter strength Promoter strength- measure of how strongly is RNAP bound to the promoter Strong promoter high frequency of initiation of transcription Weak promoter low frequency of initiation of transcription Frequency of initiation by RNAP at different promoters depends on : Promoter nucleotide sequence Presence/absence of specific factor Other factors influencing promoter strength: Regulatory proteins or molecules Additional cis elements Binding of regulatory proteins to additional cis elements can promote or prevent binding of the RNAP to the promoter and increase or decrease level of transcription - gene expression Base composition of surrounding sequence Transcriptional Events 1. RNAP moves along DNA finds a promoter; 70 subunit interacts with 10 and then 35 ( closed complex - DNA is still base-paired) 2. H-bonds need to be broken near transcriptional start site to create open complex conformational changes of RNAP- isomerization ATP is not used 2. RNAP makes abortive 10 nucleotides; 70 gets slowly released 2. RNAP holoenzyme begins to...
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This note was uploaded on 08/03/2009 for the course BIOL BIOL308 taught by Professor Miskovic during the Spring '09 term at Waterloo.

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Spring 09 lecture 17 - Various Sigma Subunits E. coli has...

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