Promoters Information about where to start transcription.
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Transcript of Promoters Information about where to start transcription.
Promoters
Information about where to start transcription
lac operon
E. Coli Promoters• E. coli has five sigma factors:• Sigma 70: Regulate expression of most genes.• Sigma 32: Regulate expression of heat shock proteins.• Sigma 28: Regulate expression of flagellar operon (involved in cell
motion).• Sigma 38: Regulate gene expression against external stresses. • Sigma 54: Regulate gene expression for nitrogen metabolism.
lacZ operon promoter
Promoters tell which strand (hence, direction) to transcribe
Note there are 6 possible Open Reading Frames (ORFs)
Universal (almost) code
Wobble pairing(I = Inosine)
Ribosome binding sites (sequences) tell ribosomes where to start translation.
Consensus, not definite
Translation
Shine-Dalgarno Motif
• Ribosome binding site located about 13 bases upstream of AUG start codon
• SD sequence is: 5’-AGGAGGU-3’
• Middle GGAG is more highly conserved
• Degree of match is positively correlated with translation rate