Theoptional E.coli prr locusencodesa latentformof phageT4-induced anticodon nuclease

ofthehosttRNALYS. We report herethemolecular cloning, nucleotide sequence andmutational analysis ofprr-associated DNA.The results indicate that prrencodes alatent formofanticodon nuclease consisting ofa coreenzyme andcognate masking agents. Theysuggest thattheT4-encoded factors of anticodon nuclease counteract theprr-encoded masking agents, thusactivating thelatent enzyme.Theencoding ofa tRNAcleavage-ligation pathway bytwoseparate genetic systems whichcohabitate E.coli may provide a cluetotheevolution ofRNA splicing mechanisms mediated byproteins.