FIG. 1.
The effect of rsbU and rsbV mutations on SigB expression in the FDA486 background. (A) Organization of the sigB operon in S. aureus. There are two well-described transcripts, one originating from the σA promoter upstream of rsbU and the other from the σB promoter upstream of rsbV. A third 3.6-kb transcript was recently described by Senn et al. (25). (B) Equivalent amounts of cell extracts (50 μg each) from FDA486 and its isogenic mutants were immunoblotted onto nitrocellulose. The blot was then probed with anti-SigB monoclonal antibody 1D1 at a 1:2,000 dilution. The protein band was then detected with goat anti-mouse antibody conjugated to alkaline phosphatase and developing substrate as previously described (6). We also examined expression of SigB in rsbW and sigB mutants of FDA486. In both cases, no SigB protein expression was detected. These immunoblot data have been previously published by one of our laboratories (24).