Regulation of penicillinase synthesis: evidence for a unified model.

The kinetics of penicillinase induction in Bacillus cereus 569 was investigated. An increase in the rate of penicillinase synthesis was demonstrated within 30 sec of the addition of inducer (benzylpenicillin); however, the maximum induced rate of penicillinase synthesis was not attained until at least 30 min after the addition of inducer. In contrast to earlier claims, a quantitative estimate showed that the penicillinase messenger ribonucleic acid (mRNA) half-life is approximately 2 min. These findings strongly suggest that the rate of synthesis of penicillinase mRNA increases continuously during most of the 30-min latent period. A model for the regulation of penicillinase synthesis in three gram-positive organisms is presented which is consistent with a nondiffusible inducer, a short-lived mRNA, a relatively long latent period (i.e., an apparently slow inactivation of penicillinase repressor), and the existence of at least two regulatory genes.