Yeast gene CDC8 encodes thymidylate kinase and is complemented by herpes thymidine kinase gene TK.

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Abstract
The herpes simplex virus type 1 thymidine kinase gene TK complements the defect in 5 temperature-sensitive mutants and in vitro constructed insertion and deletion mutants of the CDC8 gene of S. cerevisiae. The herpes thymidine kinase enzyme acts as both a thymidine kinase and a thymidylate kinase (dTMP kinase). The latter activity is responsible for the cdc8 complementation since all thermosensitive cdc8 mutants are deficient in dTMP kinase activity at all tempertures. An intragenic revertant, cdc8-320, which was selected by demanding mitotic growth at the restrictive temperature, exhibits thermolabile dTMP kinase activity. CDC8 is apparently the structural gene for dTMP kinase, which catalyzes an essential step in DNA precursor biosynthesis. The DNA replication defect of cdc8 mutants could not be bypassed by the addition of deoxyribonucleoside triphosphates to permeabilized cells. This apparent discrepancy can be explained by hypothesizing a multiprotein yeast DNA replication complex containing the CDC8 protein.