Sequence of hrdB, an essential gene encoding sigma-like transcription factor of Streptomyces coelicolor A3(2): homology to principal sigma factors.

The complete nucleotide sequence of the hrdB gene, an essential gene of Streptomyces coelicolor A3(2), indicates the presence of an open reading frame encoding a putative polypeptide of 442 amino acid (aa) residues with an Mr of 48,412. The principal sigma-like transcriptional factor of S. coelicolor (HrdB) protein showed an extensive aa sequence homology with the known principal sigma factors of Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa and Myxococcus xanthus. The degree of sequence similarity between HrdB protein and the known principal sigma factors was distinct from that observed between the principal sigma factors and the alternative (minor) sigma factors. Essentially all of the functional domains proposed for the principal sigma factor of E. coli were conserved in HrdB protein. The putative sigma factor, HrdB, like that of B. subtilis had a short internal nonconserved region, which might be characteristic of Gram+ species.