FIG. 2.

Identification and mutagenesis of a cis-acting sequence required for VirB-mediated derepression of icsB transcription. (A) The nucleotide sequences of the box 1 and 2 motifs that make up the inverted repeat in the region that was protected from DNase I digestion by VirB are shown, together with the direction of transcription of the icsB gene (arrow). (B) Summary of the mutations introduced into the box 1 and 2 sequences (underlined). Base substitutions are shown in uppercase letters, and absent bases are represented by hyphens. Construct 1 had no icsB sequences added to the gfp reporter gene in the pZep08 plasmid. The effect of these icsB regulatory sequence mutations on the VirB activation of an icsB::gfp (C) and an mxiC::lacZ (D) reporter fusion is shown. Numbers at the bottom indicate the mutated sequences. In each case (C and D), the data corresponding to sequence 2 were obtained without the addition of an arabinose inducer.