A Uracil-DNA Glycosylase Inhibitor Encoded by a Non-uracil Containing Viral DNA

Uracil-DNA glycosylase (UDG) is an enzyme involved in the base excision repair pathway. It specifically removes uracil from both single-stranded and double-stranded DNA. The genome of the Bacillus subtilis phage ϕ29 is a linear double-stranded DNA with a terminal protein covalently linked at each 5′-end. Replication of ϕ29 DNA starts by a protein-priming mechanism and generates intermediates that have long stretches of single-stranded DNA. By using in vivo chemical cross-linking and affinity chromatography techniques, we found that UDG is a cellular target for the early viral protein p56. Addition of purified protein p56 to B. subtilis extracts inhibited the endogenous UDG activity. Moreover, extracts from ϕ29-infected cells were deficient in UDG activity. We suggested that inhibition of the cellular UDG is a defense mechanism developed by ϕ29 to prevent the action of the base excision repair pathway if uracil residues arise in their replicative intermediates. Protein p56 is the first example of a UDG inhibitor encoded by a non-uracil-containing viral DNA.
This work was supported in part by Ministerio de Ciencia y Tecnología Grant BMC2002-03818 (to M. S.) and by Comunidad Autónoma de Madrid Grant GR/SAL/0087/2004 (to A. B.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.