GENETIC-EVIDENCE FOR INTERACTION OF SIGMA-A WITH 2 PROMOTERS IN BACILLUS-SUBTILIS

The specificity of promoter binding by RNA polymerase is governed by the sigma subunit. Recent studies, in which single-amino-acid substitutions in sigma factors have been found to suppress the effects of specific base pair substitutions in promoters, support the model that these sigma factors make sequence-specific contacts with nucleotides at the -10 and -35 regions of promoters. We found that single-amino-acid substitutions in the putative -35 region and -10 region recognition domains of sigma-A specifically suppressed the effects of mutations in the -35 and -10 regions, respectively, of two promoters that are expressed in exponentially growing Bacillus subtilis. These mutations change the specificity of sigma-A, the primary sigma factor in growing B. subtilis, and demonstrate that this sigma factor interacts with promoters in a manner similar to that of its homolog in Escherichia coli, sigma-70. These mutant derivatives of sigma-A also provide a tool that may be useful for determining whether sigma-A uses specific promoters in vivo.