FIG. 3.

VirB requires the box 2 sequence to bind to the icsB regulatory region. Electrophoretic mobility shift assays were carried out with icsB regulatory-region DNA containing the wild-type sequence (2) and mutant derivative sequences (9 and 10). The concentrations of purified VirB protein used are shown above the lanes. Arrows at the right indicate the positions of the free probe and VirB-DNA complexes. The purified VirB protein did not shift the mobility of a nonspecific DNA sequence from within the open reading frame of the S. flexneri icsP gene (31) under these conditions (data not shown).