(a) The promoter lies “upstream” (toward the 5′ end) of the initiation point and coding sequences. (b) Promoters have regions of similar sequences, as indicated by the yellow shading in seven different promoter sequences in E. coli. Spaces (dots) are inserted in the sequences to optimize the alignment of the common sequences. Numbers refer to the number of bases before (−) or after (+) the RNA synthesis initiation point. The consensus sequence for most E. coli promoters is at the bottom.