Fig. 3.

Partial derepression of the proU promoter by VirB. Summaries of the structures of various derivatives of the E. coli proU promoter region are presented at the left; levels of expression of the proU-gfp transcriptional reporter fusion are given at the right (diagrams not to scale). Shown are the native proU promoter (A), proU with a functional VirB binding site located at position −150 (B) or with an inactivated binding site for VirB (C), and proU with a functional binding site for VirB at position −60 with the URE upstream (D) or with an inactivated binding site for VirB (E). All constructs were assessed in S. flexneri for proU-gfp expression in a virB mutant (black bars), the wild type (white bars), and the hns mutant (gray bars) under conditions normally repressive of proU transcription.