STUDIES OF THE REPRESSOR (BLAL) OF BETA-LACTAMASE SYNTHESIS IN STAPHYLOCOCCUS-AUREUS

Purified Blal, the putative repressor of the beta-lactamase operon in Staphylococcus aureus, binds specifically to two regions of dyad symme try (operators) located in the blaZ-blaR1 intergenic region. Blal bind s with similar affinity to the two regions and to the related sequence upstream of the mec gene found in methicillin-resistant strains of S. aureus, providing physical evidence for the cross-talk previously obs erved between these systems. A change from a lysine in the N-terminus of Blal to an alanine or deletion of the C-terminal 23 amino acids sev erely reduces its DNA-binding ability, demonstrating the functional im portance of both the N- and C-termini. An operator DNA-protein complex observed with crude cell lysates from repressed cells, indistinguisha ble from that observed with purified Blal, was eliminated by induction of the beta-lactamase operon. Furthermore, Blal is proteolytically cl eaved in response to the addition of inducer in a blaR1-dependent mann er, providing primary evidence for the molecular basis of induction. T hus, Blal is shown to be the repressor of the beta-lactamase system.