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Abstract
SUMMARY: Treatment of the naturally occurring magno-inducible Staphylococcus aureus strain 8325-18 with ethyl methane sulphonate allows the isolation of mutants which synthesize much less penicillinase than the parent. Both inducible and constitutive mutants can be isolated and their activities range from 0.1 to 50% of the basal activity of the wild type. All the mutants examined here synthesize a penicillinase indistinguishable from the wild type in terms of substrate profile and reaction with specific anti-exo-penicillinase serum. Examination of the genetic make-up of the mutants shows that they all possess an intact inducibility (i +) gene. It is theoretically possible that the lesion in the micro-inducible strains could lie in the penicillinase structural gene, but such a location is extremely unlikely for the micro-constitutives. The most likely location for these mutants is a region analogous to the operator of the lactose segment of Escherichia coli; however, their properties are incompatible with the recent suggestion that the operator region should be divided into two distinct parts.
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