sigma E changed to sigma B specificity by amino acid substitutions in its -10 binding region

The association of a sigma factor (sigma) with RNA polymerase in bacteria determines its specificity of promoter utilization. To identify amino acid residues in sigma E from Bacillus subtilis that determine the specificity of its interaction with the nucleotides at the -10 region of its cognate promoters, we tested whether base pair substitutions in the -10 region of a sigma B-dependent promoter could signal its utilization by sigma E-RNA polymerase. We found that a combination of base pair substitutions at positions -15 and -14 of the sigma B-dependent ctc promoter resulted in its utilization by sigma E-RNA polymerase in vivo. We also found that the combination of two amino acid substitutions at positions 119 and 120 in sigma E changed its specificity for promoter utilization, resulting in a sigma factor that directed transcription from the sigma B-dependent ctc promoter, but not from sigma E-dependent promoters. These results suggest that amino acid residues at positions 119 and 120 determine, at least in part, the specificity of interactions between sigma E and the nucleotides in the -10 region of its cognate promoters.