Transcriptional regulator acting as an intermediary between major regulators sarA and agr and virulence genes. Represses alpha-hemolysin (hla) gene expression. Down-regulates agr RNAIII expression by repressing sarU, a positive activator of agr expression. Up-regulates sarS, which induces the expression of the cell wall-associated protein A (spa). Repressed by SarA and agr, particularly in the post-exponential phase. Belongs to the SarA family.