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 Bord etella pertussis. The deduced amino acid sequence reveals a protein of 733 residues which has extensive amino acid homology with the princip al a factors of a number of divergent prokaryotes. It is larger than m ost a factors identified to date, having a molecular mass of 81.3 kDa. We have designated this factor sigma 80. In a heterologous complement ation assay, B. pertussis rpoD was able to complement the Escherichia coli rpoD temperature sensitive mutant UQ285. Furthermore, B. pertussi s rpoD conferred better specificity to the E. coli RNA polymerase, all owing increased expression of the B. pertussis virulence-associated fh a promoter, but could not activate the ptx and cya promoters in the E. coli UQ285 strains carrying the B. pertussis bvg locus. We discuss th e implications of these results on the mechanisms involved in the acti vation of virulence-associated promoters.