Gene encoding the sigma 37 species of RNA polymerase sigma factor from Bacillus subtilis

sigma 37 is a minor species of RNA polymerase sigma factor found in the Gram-positive bacterium Bacillus subtilis. sigma 37 governs the transcription in vitro of genes that are turned on at an early stage in spore formation, as well as other genes that are switched on at the end of the exponential phase of growth but that are not under sporulation control. To study the role of sigma 37 in B. subtilis gene expression, we have cloned the gene for this minor species of sigma factor in Escherichia coli by using as a hybridization probe a synthetic oligonucleotide that was designed on the basis of the NH2-terminal amino acid sequence of sigma 37 protein. We determined the nucleotide sequence of the entire sigma 37 gene, which was found to encode a 262-amino acid residue polypeptide of 29.9 kDa. The predicted amino acid sequence of sigma 37 showed significant homology to that of other sigma proteins in a region that has been proposed to be the site of binding of these factors to core RNA polymerase. Genetic mapping experiments placed the gene for sigma 37, herein designated sigB, at 40 degrees on the genetic map of Piggot and Hoch [Piggot, P. & Hoch, J. A. (1985) Microbiol. Rev. 49, 158-179]. An insertion mutation was constructed in sigB and found not to impair growth or sporulation.