CONSTRUCTION OF A VACCINIA VIRUS DEFICIENT IN THE ESSENTIAL DNA-REPAIR ENZYME URACIL DNA GLYCOSYLASE BY A COMPLEMENTING CELL-LINE

The vaccinia virus D4R open reading frame, encoding the essential DNA repair enzyme uracil DNA glycosylase, was expressed in two permanent c ell lines, the rabbit kidney cell line RK13 and the human fibroblast c ell line 293. The temperature-sensitive vaccinia virus mutant ts4149, which maps within D4R, was able to grow under restrictive conditions i n both of these transformed cell lines, Cell clones complemented D4R f unction to various degrees, demonstrating complementation of an essent ial vaccinia virus gene by a cell line constitutively expressing the e ssential function, Thus, the complementing host cells allowed the resc ue of a virus defective in the D4R gene, demonstrating that this syste m may he used for the propagation of defective cytoplasmic DNA viruses . The defective virus grew to high yields only in the engineered cell lines, The data support the hypothesis that early gene products, such as uracil DNA glycosylase, supplied in trans can fully complement esse ntial viral functions.