REGULATION OF ALPHA-HEMOLYSINS AND BETA-HEMOLYSINS BY THE SAR LOCUS OF STAPHYLOCOCCUS-AUREUS

We recently identified a locus on the Staphylococcus aureus chromosome , designated sar, for staphylococcal accessory regulator, that is invo lved in the global regulation of extracellular and cell wall-associate d proteins. Previous phenotypic and Southern blot analyses with Tn917 and agr probes indicated that this locus is distinct from agr, a previ ously described global regulator of exoproteins in S. aureus. To under stand the mode of regulatory control of exoprotein synthesis by the sa r locus, the sar genotype was transduced from the original sar mutant 11D2 into two prototypic S. aureus strains, RN6390 and RN450, with wel l-defined genetic backgrounds. An analysis of extracellular protein pr ofiles by use of silver-stained sodium dodecyl sulfate gels revealed a lterations in the pattern of exoprotein production in the late log-ear ly stationary phase in the sar mutants in comparison with the correspo nding parents. In addition, most of the phenotypic changes that occurr ed in the conversion from the sar(+) genotype to the sar genotype in m utant 11D2 were also found in these mutants. Northern (RNA) blot analy ses of two exoprotein transcripts (alpha- and beta-hemolysins) from st rain RN6390 and its corresponding sar mutant revealed dowregulation of these transcripts in the mutant. Serial studies of these hemolysin tr anscripts at various growth intervals demonstrated that the transcript ional regulation of the hemolysin genes by the sar locus began during the log phase and continued into the postexponential phase. These data suggested that the snr locus probably regulates exoprotein genes at t he transcriptional level. This mode of regulation is similar to that o f exoprotein target gene transcription by agr.