Analysis of the different molecular forms of penicillin-binding protein 1B in Escherichia coli ponB mutants...

Penicillin-binding protein (pbp) 1b, the main DD-transpeptidase/transglycosylase of Escherichia coli, is normally present in the cell in three molecular forms alpha, beta and gamma, differentiated by their mobility in sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The three molecular forms are enzymatically active in vitro and their relative amounts are kept fairly constant in most labelling experiments with radioactive beta-lactam antibiotics. In this paper, we have analyzed the expression of ponB (mrcB), the structural gene for pbp 1b, and the relation among the three forms of pbp 1b in ponB strains lysogenyzed by lambda 540 (ponB+) recombinant bacteriophages. Our data indicate that ponB is transcribed anti-clockwise on the E. coli chromosome and suggest that pbp 1b alpha is the first membrane-bound form of pbp 1b able to bind labelled beta-lactams, and is the precursor of pbp 1b beta which is, in turn, the precursor of pbp 1 beta gamma.