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

The precise start points for transcription of the blaZ and of the blaRl/bla l genes of the Staphylococcus aureus beta -lactamase operon have been deter mined by primer extension analysis. Consequently the overlapping promoter s equences 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 sa me mRNA as the blaRl probe. The gene cat, encoding chloramphenicol acetyltr ansferase, was fused separately to the blaZ and blaRl/blal promoters, and u sed to compare their strengths. The promoter for blaZ is about six times st ronger than that for blaRl/blal and the synthesis of chloramphenicol acetyl transferase from both promoters is inducible, supporting the results from t he Northern blots.