FIG. 1.

Base sequence of the wild-type E. coli gal operon regulatory region, showing the two overlapping promoters P1 and P2. The sequence is numbered with the P1 transcript start as +1. Above the sequence are shown the various P1 elements: the 22-bp DNA site for CRP and the −35 and extended −10 elements. Below the sequence are shown the P2 −35 and extended −10 element and the P2 start point. The location of the p19T substitution, which completely inactivates P2, is indicated. With the gal regulatory region carrying the p19T substitution, RNAP initiates transcription at P1 in both the absence and the presence of CRP.