CHARACTERIZATION OF THE SAR LOCUS AND ITS INTERACTION WITH AGR IN STAPHYLOCOCCUS-AUREUS

The expression of cell wall and extracellular proteins in Staphylococc us aureus is controlled by global regulatory systems, including sar an d agr. We have previously shown that a transposon insertion into the 3 72-bp sarA gene within the sar Locus resulted in decreased expression of several extracellular and cell wall proteins (A. L. Cheung and S. J . Projan, J. Bacteriol. 176:4168-1172, 1994). In this study, Northern (RNA blot) analysis with a 732-bp sarA probe indicated that two major transcripts (0.56 and 1.2 kb) were absent in the sar mutant compared d th the parental strain RN6390. Additional transcriptional studies reve aled that the sarA gene is encoded within the 0.56-kb transcript. Nota bly, a plasmid carrying the sarA gene together with a 1.2-kb upstream fragment (1.7 kb total) was able to reestablish the 1.2-kb transcript in the mutant. Although reconstitution of the parental phenotype by th e sarA gene was incomplete, the introduction of a plasmid carrying the 1.7-kb fragment to the mutant restored the parental phenotype. Transc ription of RNAII and RNAIII, which encode the structural and regulator y genes of agr, respectively, was diminished in the mutant but restore d to wild-type levels by complementation with the 1.7-kb fragment. In gel shift assays, cell extracts of this clone were able to retard the mobility of a labeled RNAII promoter probe hut not an RNAIII promoter element, These data suggest that sarA and the adjacent upstream DNA ar e essential to the expression of a DNA-binding protein(s) with specifi city for the RNAII promoter. thereby controlling agr-related transcrip tion.