Expression of the Herpes simplex virus thymidine kinase gene in Saccharomyces cerevisiae

Yeast plasmids have been constructed that carry the Herpes simplex Virus type 1 (HSV-1) thymidine kinase (TK) gene which is functionally expressed in Saccharomyces cerevisiae. The expression of the TK gene appears to be due to transcriptional read-through from a yeast promoter that lies on the 3' side of the HIS3 gene. The TK+ yeast possesses in vitro thymidine kinase activity which is absent in the original yeast strain. Yeast strains auxotrophic for thymidine monophosphate (dTMP) (tmp1) can grown on thymidine-containing medium after transformation with these plasmids. Tmp+, TK+ S. cerevisiae whose de novo synthesis of dTMP is inhibited with amethopterin plus sufanilamide is also capable of growth in thymidine. S. cerevisiae transformed with such plasmids is capable of incorporating thymidine and bromodeoxyuridine into DNA.