Dispensability of either penicillin-binding protein-1a or -1b involved in the essential process for cell elongation in Escherichia coli.

A strain of Escherichia coli lacking the entire ponB gene and a strain lacking the proximal part of the ponA gene were constructed by substitution with a drug resistance gene. These strains lost either penicillin-binding protein(PBP) -1b or -1a totally and their growth was apparently normal at 30°C and 42°C except that growth of the ponB deletion strain was poor on a nutrient agar plate containing no NaCl at 30°C as well as at 42°C. Transductional experiments to introduce the ponB deletion into the ponA deletion strain, and vice versa, showed that the ponA ponB double deletion was lethal unless the deletion was functionally compensated, e.g., by the presence of a plasmid carrying either gene. Thus, either PBP-1b (ponB) or PBP-1a (ponA), but not both, is dispensable for cell viability, at least under ordinary culture conditions. Transductional experiments also suggested that the γ component of PBP-1b or the PBP-1b lacking the C-terminal portion encoded in the distal region to the SphI site on the ponB was sufficient for supporting growth of the E. coli cell.