REGULATION OF PROTEIN-A SYNTHESIS BY THE SAR AND AGR LOCI OF STAPHYLOCOCCUS-AUREUS

The synthesis of protein A in Staphylococcus aureus is regulated by gl obal regulatory loci such as sar and agr. Phenotypic data indicate tha t both sar and agr suppress protein A synthesis; like agr, sar also re gulates protein A production at the transcriptional level, To determin e the genetic requirement of sar in protein A suppression, we transfor med shuttle plasmids containing various sar fragments into a snr mutan t, Our results indicated that the 560-bp sarA transcript, or, more pro bably, the SarA protein (13.5 kDa), is sufficient for suppressing prot ein A gene transcription when introduced on a multicopy plasmid or as a single copy in the chromosome. Immunoblot analysis with a chicken an ti-protein A antibody also confirmed the reduction in protein A expres sion in these snr mutant clones. Complementation studies revealed that the transcription of the protein A gene can be suppressed in a sar mu tant background by a plasmid containing RNAIII, Surprisingly, in agr d eletion mutant clones and in clones derived from the agr-snr double mu tant, protein A gene transcription can also be suppressed by plasmids containing the sarA transcript plus additional upstream sequence but n ot the sarA transcript alone, These data suggest that the snr locus ca n down-modulate protein A gene transcription via both RNAIII-dependent and RNAIII-independent pathways, Consistent with the hypothesis of an RNAIII-independent pathway is an additional genetic requirement for p rotein A suppression in the agr deletion mutant RN6911 as well as the isogenic double snr-agr mutant, whereas in the snr mutant background, the sarA transcript encoding the SarA protein alone is sufficient, The se data suggested that both snr and agr are coregulators of protein A synthesis in S. aureus.