Cloning and characterization of mepA, the structural gene of the penicillin-insensitive murein endopeptidase from Escherichia coli

The putative structural gene mepA of the penicillin-insensitive murein endopeptidase from Escherichia coli was cloned and sequenced. N-terminal sequence determination with the isolated endopeptidase protein showed that this enzyme is coded by the mepA gene and that it is synthesized initially with an N-terminal signal peptide. No significant sequence homology with the other (penicillin-sensitive) murein endopeptidase (dacB) or any other protein was found. The precise chromosomal mapping position of mepA relative to two other genes, aroC and fabB, was shown to be 50.4 min. E. coli strains carrying multicopy plasmids with the mepA gene produced 5-6-fold more endopeptidase and secreted it into the periplasm, where it appeared to function normally in vivo since the release of cell wall peptides into the medium increased in parallel. The transformed cells were, however, not unusually sensitive to penicillin and their murein had a normal degree of cross-bridges.