SIGMA-B, A PUTATIVE OPERON ENCODING ALTERNATE SIGMA-FACTOR OF STAPHYLOCOCCUS-AUREUS RNA-POLYMERASE - MOLECULAR-CLONING AND DNA-SEQUENCING

We have identified a gene cluster located on the chromosomal SmaI I fr agment of a highly methicillin resistant strain of Staphylococcus aure us, consisting of four open reading frames (ORFs), named after the num ber of deduced amino acid residues, in the sequential order orf333-orf 108-orf159-orf256. The gene cluster showed close similarities to the B acillus subtilis sigB operon both in overall organization and in prima ry sequences of the gene products. The complete gene cluster (provisio nally named sigma-B or sigR) was preceded by an sigma(A)-like promoter (P-A) and had an internal sigma(B)-like promoter sequence (P-B) betwe en orf333 and orf108, suggesting a complex regulatory mechanism. The p olypeptides encoded by orf333, -108, -159, and -256 showed 62, 67, 71, and 77% homologies, respectively, with the RsbU, RsbV, RsbW, and SigB polypeptides encoded by the B. subtilis sigB operon. A Tn551 insertio nal mutant, RUSA168 (insert in orf256 of the staphylococcal sigma-B op eron) showed drastic reduction in methicillin resistance (decrease in MIC from 1,600 mu g ml(-1) to 12 to 25 mu g ml(-1)).