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

The repressor proteins BlaI and MecI bind similarly to the bla operator implicated in the regulation of beta-lactamase synthesis in Staphylococcus aureus. BlaI 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 BlaI molecules bound at the dyads probably do not cause bending or looping of the intervening DNA. DMS protection assays of BlaI 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 initiator. Explanations for this are considered.