The Bordetella pertussis sigma subunit of RNA polymerase confers enhanced expression of fha in Escherichia coli.

We have cloned the rpoD gene coding for the major sigma factor of Bordetella pertussis. The deduced amino acid sequence reveals a protein of 733 residues which has extensive amino acid homology with the principal sigma factors of a number of divergent prokaryotes. It is larger than most sigma factors identified to date, having a molecular mass of 81.3 kDa. We have designated this factor sigma 80. In a heterologous complementation assay, B. pertussis rpoD was able to complement the Escherichia coli rpoD temperature-sensitive mutant UQ285. Furthermore, B. pertussis rpoD conferred better specificity to the E. coli RNA polymerase, allowing increased expression of the B. pertussis virulence-associated tha promoter, but could not activate the ptx and cya promoters in the E. coli UQ285 strains carrying the B. pertussis bvg locus. We discuss the implications of these results on the mechanisms involved in the activation of virulence-associated promoters.