Enteric virulence associated protein VapC inhibits translation by cleavage of initiator tRNA

Eukaryotic PIN (PilT N-terminal) domain proteins are ribonucleases involved in quality control, metabolism and maturation of mRNA and rRNA. The majority of prokaryotic PIN-domain proteins are encoded by the abundant vapBC toxin--antitoxin loci and inhibit translation by an unknown mechanism. Here we show that enteric VapCs are site-specific endonucleases that cleave tRNAfMet in the anticodon stem-loop between nucleotides +38 and +39 in vivo and in vitro. Consistently, VapC inhibited translation in vivo and in vitro. Translation-reactions could be reactivated by the addition of VapB and extra charged tRNAfMet. Similarly, ectopic production of tRNAfMet counteracted VapC in vivo. Thus, tRNAfMet is the only cellular target of VapC. Depletion of tRNAfMet by vapC induction was bacteriostatic and stimulated ectopic translation initiation at elongator codons. Moreover, addition of chloramphenicol to cells carrying vapBC induced VapC activity. Thus, by cleavage of tRNAfMet, VapC simultaneously may regulate global cellular translation and reprogram translation initiation.