Phage T4-coded Stp: Double-edged effector of coupled DNA and tRNA-restriction systems

Michal Penner, Ilan Morad, Larry Snyder, Gabriel Kaufmann*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


The optional Escherichia coli prr locus encodes two physically associated restriction systems: the type IC DNA restriction-modification enzyme EcoprrI and the tRNA(Lys)-specific anticodon nuclease, specified by the PrrC polypeptide. Anticodon nuclease is kept latent as a result of this interaction. The activation of anticodon nuclease, upon infection by phage T4, may cause depletion of tRNA(Lys) and, consequently, abolition of T4 protein synthesis. However, this effect is counteracted by the repair of tRNA(Lys) in consecutive reactions catalysed by the phage enzymes polynucleotide kinase and RNA ligase. Stp, a short polypeptide encoded by phage T4, has been implicated with activation of the anticodon nuclease. Here we confirm this notion and also demonstrate a second function of Stp: inhibition of EcoprrI restriction. Both effects depend, in general, on the same residues within the N-proximal 18 residue region of Stp. We propose that Stp 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.

Original languageEnglish
Pages (from-to)857-868
Number of pages12
JournalJournal of Molecular Biology
Issue number5
StatePublished - 23 Jun 1995


FundersFunder number
Israel National Science Foundation
Israeli Ministry of Arts and Sciences
Levi Eshkol Foundation
National Science Foundation


    • Anticodon nuclease
    • Hsd
    • Polynucleotide kinase
    • RNA ligase
    • Trna(Lys)


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