FIG. 2.

DNA sequence of the potential PtxS operator (dyad symmetry) site within the ptxS upstream region. Boxed regions indicate the right (bottom, 3′ sense sequence) and left (top, 5′ antisense sequence) halves of the dyad symmetry. The nucleotides are numbered (1 to 7) for the right half and (1′ to 7′) for the left half. Filled circles indicate the positions of the nucleotides that were mutated in this study. The types of the mutations are indicated. Plasmids that carry either deletion of the dyad symmetrical sequence or specific nucleotide mutations were divided into two groups. In group I, the deletion and individual mutations were generated in plasmid pBS9 (which carries the 722-bp fragment) by site-directed mutagenesis. For expression experiments, the 722-bp BamHI/KpnI fragment was deleted from pBS8 and replaced by either the 708-bp BamHI/KpnI fragment from pBS9 or the 722-bp BamHI/KpnI fragments from pBS9 derivatives (group II). Plasmid pBS8 is the same as the previously described plasmid pBS8-4 (15).