Effects of vaccinia virus uracil DNA glycosylase catalytic site and deoxyuridine triphosphatase deletion mutations individually and together on replication in active and quiescent cells and pathogenesis in mice

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Abstract
Low levels of uracil in DNA result from misincorporation of dUMP or cytosine deamination. Vaccinia virus (VACV), the prototype poxvirus, encodes two enzymes that can potentially reduce the amount of uracil in DNA. Deoxyuridine triphosphatase (dUTPase) hydrolyzes dUTP, generating dUMP for biosynthesis of thymidine nucleotides while decreasing the availability of dUTP for misincorporation; uracil DNA glycosylase (UNG) cleaves uracil N-glycosylic bonds in DNA initiating base excision repair. Studies with actively dividing cells showed that the VACV UNG protein is required for DNA replication but the UNG catalytic site is not, whereas the dUTPase gene can be deleted without impairing virus replication. Recombinant VACV with an UNG catalytic site mutation was attenuated in vivo, while a dUTPase deletion mutant was not. However, the importance of the two enzymes for replication in quiescent cells, their possible synergy and roles in virulence have not been fully assessed.