Escherichia coli peptidase A, B, or N can process translation inhibitor microcin C

The heptapeptide-nucleotide microcin C (McC) targets aspartyl-tRNA synthetase. Upon its entry into a susceptible cell, McC is processed to release a nonhydrolyzable aspartyl-adenylate that inhibits aspartyl-tRNA synthetase, leading to the cessation of translation and cell growth. Here, we surveyed Escherichia coli cells with singly, doubly, and triply disrupted broad-specificity peptidase genes to show that any of three nonspecific oligopeptidases (PepA, PepB, or PepN) can effectively process McC. We also show that the rate-limiting step of McC processing in vitro is deformylation of the first methionine residue of McC.