<p>Thymidylate kinase (<db_xref db="EC" dbkey="2.7.4.9"/>; dTMP kinase) catalyzes the phosphorylation of thymidine 5'-monophosphate (dTMP) to form thymidine 5'-diphosphate (dTDP) in the presence of ATP and magnesium: </p><reaction>ATP + thymidine 5'-phosphate = ADP + thymidine 5'-diphosphate </reaction><p>Thymidylate kinase is an ubiquitous enzyme of about 25 Kd and is important in the dTTP synthesis pathway for DNA synthesis. The function of dTMP kinase in eukaryotes comes from the study of a cell cycle mutant, cdc8, in <taxon tax_id="4932">Saccharomyces cerevisiae</taxon>. Structural and functional analyses suggest that the cDNA codes for authentic human dTMP kinase. The mRNA levels and enzyme activities corresponded to cell cycle progression and cell growth stages[<cite idref="PUB00016913"/>]. </p>