Studies of the operator region of the Staphylococcus aureus beta-lactamaseoperon

The repressor proteins BlaI and MecI bind similarly to the bla operator imp licated in the regulation of beta -lactamase synthesis in Staphylococcus au reus. Dial binds to two separate dyads but neither copper-phenanthroline fo otprinting nor dimethyl sulphate (DMS) methylation protection assays produc ed any evidence of a change in the geometry of the DNA between the two dyad s. It is concluded that BlaI molecules bound at the dyads probably do not c ause bending or looping of the intervening DNA. DMS protection assays of Bl aI 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 b laZ gene resulted in decreased synthesis of the chloramphenicol acetyltrans ferase reporter protein synthesized from the blaZ promoter/translation init itiator. Explanations for this are considered.