The-10 region is a key promoter specificity determinant for the bacillus subtilis extracytoplasmic-function sigma(x) and sigma(w)

Transcriptional selectivity derives, in large part, from the sequence-speci fic DNA-binding properties of the sigma subunit of RNA polymerase. There ar e 17 sigma factors in Bacillus subtilis which, in general, recognize distin ct sets of promoters. However, some sigma factors have overlapping promoter selectivity. We hypothesize that the overlap between the regulons activate d by the sigma (x) and sigma (w) factors can be explained by overlapping sp ecificity for the -10 region: sigma (x) recognizes - 10 elements with the s equence CGAC and sigma (w) recognizes CGTA, while both can potentially reco gnize CGTC. To test this model, we mutated the sigma -specific autoregulato ry site (P-x), containing the -10 element CGAC, to either CGTC or GCTA. Con versely, the sigma (w) autoregulatory site (P-w) was altered from CGTA to C GTC or CGAC. Transcriptional analyses, both in vitro and in vivo, indicate that changes to the -10 element are sufficient to switch a promoter from th e sigma (x) to the sigma (w) regulon or, conversely, from the sigma (w) to the sigma (x) regulon, but context effects clearly play an important role i n determining promoter strength. It seems likely that these subtle differen ces in promoter selectivity derive from amino acid differences in conserved region 2 of sigma, which contacts the -10 element. However, we were unable to alter promoter selectivity by replacements of two candidate recognition residues in sigma (w).