Studies of the operator region of the Staphylococcus aureus β-lactamase operon

Abstract

The repressor proteins Blal and Mecl bind similarly to the bla operator implicated in the regulation of β-lactamase synthesis in Staphylococcus aureus. Blal binds to two separate dyads but neither copper-phenanthroline footprinting nor dimethyl sulphate (DMS) methylation protection assays produced any evidence of a change in the geometry of the DNA between the two dyads. It is concluded that Blal molecules bound at the dyads probably do not cause bending or looping of the intervening DNA. DMS protection assays of Blal binding to the bla operator in vitro and in vivo gave similar results so that it is tentatively concluded that the in vitro results are an accurate reflection of the in vivo situation. Deletion of the dyad nearest to the blaZ gene resulted in decreased synthesis of the chloramphenicol acetyltransferase reporter protein synthesized from the blaZ promoter/translation inititiator. Explanations for this are considered.