The signal transducer (BlaRI) and the repressor (Blal) of the Staphylococcus aureus β-lactamase operon are inducible

The precise start points for transcription of the blaZ and of the blaRl/blal genes of the Staphylococcus aureus beta -lactamase operon have been determined by primer extension analysis. Consequently the overlapping promoter sequences were deduced. Northern blots showed that the synthesis of the 2100 nt mRNA from blaRl is inducible and that a blal probe hybridized to the same mRNA as the blaRl probe. The gene cat, encoding chloramphenicol acetyltransferase, was fused separately to the blaZ and blaRl/blal promoters, and used to compare their strengths. The promoter for blaZ is about six times stronger than that for blaRl/blal and the synthesis of chloramphenicol acetyltransferase from both promoters is inducible, supporting the results from the Northern blots.