Figure 7.

CtpA is a possible negative regulator of SosA. A. Hypersusceptibility of an S. aureus JE2 ctpA mutant to SosA‐mediated growth inhibition. Expression of sosA (pSosA) in WT S. aureus JE2 and the corresponding JE2‐ctpA mutant (ctpA) were compared and referenced to the vector control (vector) and expression of the hyperactive SosAd10 variant (pSosAd10) in the WT. Cells were grown exponentially to an OD₆₀₀ of 0.5, serially 10‐fold diluted and plated on TSA (Control) or TSA plus inducer (AHT) at indicated concentrations. The plates were incubated overnight at 37°C and imaged. B. Assessment of mitomycin C susceptibility of a ctpA mutant by comparison of plating efficiency of S. aureus 8325‐4 and JE2 WT, ctpA and ΔsosA‐ctpA in presence of 0.5 µg ml⁻¹ MMC. Cells were grown exponentially to an OD₆₀₀ of 0.5 and serially 10‐fold diluted before plating and incubation at 37°C overnight. C. Western blot of accumulated SosA in S. aureus 8325‐4 WT and the ctpA mutant at indicated time points after the addition of 1 µg ml⁻¹ of MMC to exponentially growing cells. The full blot is displayed in Fig. S5 and may serve as a control for equal loading and transfer by comparing intensities of nonspecific high molecular weight bands.