IDENTIFICATION OF A POXVIRUS GENE ENCODING A URACIL DNA GLYCOSYLASE

An open reading frame, BamHI D6R, from the central highly conserved re gion of the Shope fibroma virus (SFV) genome was sequenced and found t o have significant homology to that of uracil DNA glycosylases from a number of organisms. Uracil DNA glycosylase catalyzes the initial step in the repair pathway that removes potentially mutagenic uracil from duplex DNA. The D6R polypeptide was expressed in reticulocyte lysates programed with RNA transcribed from an expression vector containing th e T7 RNA polymerase promoter. A highly specific ethidium bromide fluor escence assay of the in vitro translation product determined that the encoded protein does indeed possess uracil DNA glycosylase activity. O pen reading frames from other poxviruses, including vaccinia virus (Hi ndIII D4R) and fowlpox (D4), are highly homologous to D6R of SFV and a re predicted to encode uracil DNA glycosylases. Identification of the SFV uracil DNA glycosylase provides evidence that this poxviral protei n is involved in the repair of the viral DNA genome. Since this enzyme performs only the initial step required for the removal of uracil fro m DNA, creating an apyrimidinic site, we suggest that other, possibly virus-encoded, repair activities must be present in the cytoplasm of i nfected cells to complete the uracil excision repair pathway.