TRANSCRIPTION OF STAPHYLOCOCCUS-AUREUS FIBRONECTIN-BINDING PROTEIN GENES IS NEGATIVELY REGULATED BY AGR AND AN AGR-INDEPENDENT MECHANISM

The production of cell surface proteins in Staphylococcus aureus is ge nerally down-regulated in the postex-ponential growth phase by the glo bal regulator agr. The effector of this regulation is the RNAIII molec ule, which is encoded within the agr locus. RNAIII seems to regulate m ost target genes at the level of transcription, but it also has an eff ect on the translation of some genes. To study the role of agr on the expression of fibronectin binding proteins (FnBPs), we investigated th e transcription and translation of fnb genes in agr mutant strain WA25 0 and its parent strain, 8325-4. The results show that fnb genes are n egatively regulated by ngr and also by an agr-independent mechanism th at restricts fnb mRNA synthesis to the early exponential phase of grow th. Transcription and Western blot analysis of cell-associated FnBPs d emonstrated that synthesis of both FnBPA and FnBPB in the wild-type an d agr mutant strains took place preferentially during the first hour o f growth and rapidly decreased after the second hour. We also confirme d previous results shelving that the agr mutant strain has an increase d capacity to bind fibronectin compared to its parent agr(+) strain. H owever, while the concentrations of fnb mRNAs and proteins differed by a factor of 16 between the strains, the difference in fibronectin bin ding was only twofold, indicating that the binding of fibronectin to t he bacteria is not proportional to the amount of FnBPs on their surfac e.