Function
Anticodon nuclease cleaves the tRNA(Lys). It cleaves near a pyrimidine base to generate 2':3'-P> and 5'-OH termini. Stp activates the host prrC protein probably by counteracting prr masking. Stp also inhibits EcoprrI restriction. Stp probably alters the conformation of EcoprrI and, consequently, of prrC, allowing activation of the latent anticodon nuclease. Presumably, stp evolved to offset a DNA restriction system of the host cell but was turned, eventually, against the phage as an activator of the appended tRNA restriction enzyme.