Properties of a novel thymidine kinase induced by an acyclovir-resistant herpes simplex virus type 1 mutant

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Abstract
The acyclovir-resistant mutant of herpes simplex virus type 1, SC16 S1, induced reduced levels of thymidine kinase activity (.apprx. 25% reduction) in infected hamster kidney BHK cells. The activity appeared with kinetics similar to that in wild type-infected cells and pulse-labeling experiments showed that the thymidine kinase polypeptide was synthesized at a similar rate. The enzyme was virus specific by inactivating it with antiserum raised against herpes simplex virus-infected cell proteins. The enzyme induced by the mutant had reduced electrophoretic mobility in nondenaturing gels, decreased thermal stability and decreased affinity for several different substrates (assessed by measurement of Km values) compared with the enzyme induced by the wild type. The thymidine kinase induced by the mutant apparently has an altered specificity, probably resulting from an amino acid substitution which affects the primary binding site for nucleosides and nucleoside analogs.