OVERPRODUCTION OF PENICILLIN-BINDING PROTEIN-7 SUPPRESSES THERMOSENSITIVE GROWTH DEFECT AT LOW OSMOLARITY DUE TO AN SPR MUTATION OF ESCHERICHIA-COLI

Escherichia coli Delta prc mutants lacking periplasmic protease Pre, w hich was originally found involved in the C-terminal processing of pen icillin-binding protein (PBP) 3, show thermosensitive growth at low os molarity. We isolated thermoresistant revertants containing extragenic suppressor (spr) mutations, In the prc(+) background the mutations al so caused thermosensitivity at low osmolarity, They were all mapped at about 48 min on the chromosome and most probably allelic to one anoth er, From this chromosomal region we cloned a gene that could correct t he thermosensitive defect of an spr mutant, which turned out to be a m ulticopy suppressor of spr, Analysis of the nucleotide sequence predic ted that the gene would code for a low-molecular-weight PBP, and penic illin-binding experiments revealed the product to be PBP 7, Disruption of the gene on the chromosome caused no apparent growth defect, PBP 7 seemed to be degraded by protease Pre. Overproduction of mutant PBP 7 that had the active site serine residue replaced with alanine did not correct the spr thermosensitivity, suggesting importance of the DD-en dopeptidase activity in the multicopy suppression.