Multiple paralogous genes related to the Streptomyces coelicolor developmental regulatory gene whiB are present in Streptomyces and other actinomycetes

The whiB sporulation gene of Streptomyces coelicolor was shown to encode a small, cysteine-rich putative transcription factor unlike any that had keen described previously. The large database of DNA sequences of mycobacteria (like Streptomyces, members of the Actinomycetales) has revealed a family of genes encoding proteins related to WhiB. Mycobacterium tuberculosis contains at least six such genes (whiB homologues in mycobacteria: whmA-F) and a likely seventh, whmG. Using conserved features of Whm proteins, a PCR-based approach led to the discovery that S. coelicolor A3(2) contains several similar genes. Cloning and sequencing of these whiB-like (wbl) genes revealed likely orthologues of four of the whm genes of M. tuberculosis. In all, S. coelicolor contains at least five wbl genes in addition to whiB itself. All five were shown by RT-PCR to be transcribed. A Southern blotting survey using each wbl gene as a probe showed that nearly all of a series of representatives of ten actinomycete genera (including morphologically simple organisms) contain close homologues of several wbl genes, suggesting that the ancient progenitor of all these organisms already contained a family of such genes, which have not been found in any other organisms.