Resistance of Escherichia coli to penicillins: identification of the structural gene for the chromosomal penicillinase.

A screening procedure was used to isolate a number of mutants of Escherichia coli K-12 with low penicillinase activity. By co-transduction with purA, three of the mutants were found to map near 82 min. Penicillinase was purified from one mutant and from a transductant with a temperature-sensitive enzyme. Comparison with wild-type penicillinase revealed similarities in the Ouchterlony immunodiffusion test but differences in the catalytic properties. It is concluded that the mutations have occurred in the structural gene of the chromosomal penicillinase (designated ampC). Purified enzyme and a temperature-sensitive mutant were used to investigate whether the penicillinase has a physiological function related to biosynthesis or breakdown of murein. No positive evidence for any such function was obtained.