Multiple sigma factor genes in Brevibacterium lactofermentum: characterization of sigA and sigB.

Four rpoD hybridizing signals have been identified in the chromosome of Brevibacterium lactofermentum. Two rpoD-like genes, sigA and sigB, have been cloned and sequenced, and they encode principal sigma factors of the RNA polymerase. The deduced amino acid sequences of SigA and SigB showed very high similarities to those of Mycobacterium smegmatis MysA and MysB proteins, respectively, and also to those of HrdB proteins from different Streptomyces species. SigA and SigB maintain the conserved motifs of sigma 70-like principal sigma factors. sigB is closely linked to the dtxR gene (encoding a repressor of iron-regulated promoters homologous to the diphtheria toxin repressor from Corynebacterium diphtheriae.