FIG. 1.

(a) Model for transcription activation at rhaBAD, showing the two activator proteins, cyclic AMP receptor protein (CRP) and RhaS, and RNA polymerase (RNAP) shown. The bent arrow represents the rhaBAD transcription start site. (b) DNA sequence of the RhaS binding site (rhaI). The two half-sites, rhaI₁ and rhaI₂, are inverted repeats, as indicated by the arrows above the sequence. Sequences within the half-sites are divided into two major grooves separated by a minor groove, with the outer and inner major grooves indicated. Down arrows indicate bases previously identified as important for interaction with RhaS (9); their positions relative to the rhaBAD transcription start site are indicated below. Bases overlapping the −35 region of the promoter were not analyzed in this previous study since their effects on RhaS binding and RNA polymerase binding could not easily be distinguished by the analysis used. Notice that all of the bases important in rhaI₁ are identical in rhaI₂.