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