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E - Promoter The region at start of gene which carries...

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E. coli RNA polymerase Very large protein complex, consists of five subunits 2 identical alpha subunits and 1 each of beta, beta' , and sigma The sigma subunit dissociates from the enzyme easily - leaves shortly following initiation, critical for recognition of start of gene (more shortly). holoenzyme - complete enzyme - all five subunits together but basic polymerization reaction possible without sigma subunit - core enzyme : 2 alpha, 1 beta and 1 beta' RNA polymerase so large it is visible in EM (Freifelder Fig. 9-3) (Fig. 6.1) Transcription process in 4 phases: binding of RNA polymerase at specific site of DNA [PROMOTER] where gene starts initiation elongation termination
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Unformatted text preview: Promoter The region at start of gene which carries specific binding site for RNA polymerase is called promoter The base where transcription starts is numbered +1 , bases in front or " upstream " numbered with minus sign: -1, -2, -3 and so on) A comparison of the base sequences upstream of many genes revealed similarities: -10 sequence and -35 sequence-10 consensus sequence: TATAAT (most promoters differ in one or two bases, the closer the sequence is to the consensus sequence the more efficiently the gene is transcribed) There is also a consensus sequence also for -35 sequence [ TTGACA ] (But: not all genes have the -10 and -35 sequence in promoter)...
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