Biochemical characterization of equine herpesvirus type 3-induced deoxythymidine kinase purified from lytically infected horse embryo dermal fibroblasts.

Infection of horse KyED cells with equine herpesvirus type 3 (EHV-3) resulted in a sevenfold increase in cytosol deoxythymidine kinase (dTK) activity. The EHV-3 dTK was purified from KyED cytosol dTK by affinity chromatography on deoxythymidine-Sepharose and characterized with respect to its electrophoretic mobility, molecular weight, substrate specificity, phosphate donor specificity, and immunological specificity. The purified EHV-3 dTK migrated in polyacrylamide gels with an Rf of 0.30 and sedimented in glycerol gradients with an S value of 5.13, corresponding to a molecular weight of 83,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single band with a molecular weight of 38,000 to 40,000. Antiserum prepared against the EHV-3 dTK induced in KyED cells neutralized the EHV-3-induced enzyme activity but not the dTK purified from uninfected cells. EHV-3 dTK was less sensitive to feedback inhibition to dTTP and had a lower Ki for the antiviral compound 1-beta-D-arabinofuranyosylthymine and a lower Km for the substrate deoxythymidine. These results indicate that infection of cells with EHV-3 results in the induction of a new virus-coded dTK activity which meets the criteria of Jensen for an evolutionary primitive enzyme.