Figure 1.

Identifying the function of an E. coli PBP using temperature-sensitive mutants. Most penicillins and cephalosporins inhibit E. coli cell division at low concentrations and one of the PBPs should be essential for this process. Mutants that could not divide at 42°C were isolated and screened for the production of a thermolabile PBP, by pre-incubating cell envelopes for increasing times at 42°C and examining their subsequent ability to bind radioactive penicillin when returned to 30°C. Whereas pre-incubation at 42°C does not reduce penicillin binding in the wild type (left three lanes), in this cell division mutant pre-incubation at 42°C rapidly reduces the ability of PBP 3 to bind penicillin at 30°C (right four lanes). This PBP was therefore assigned an essential role in peptidoglycan synthesis at cell division. Reproduced from reference 36 with kind permission from the American Society for Microbiology.