Thymidylate kinase (DTYMK) is a ubiquitous enzyme of about 25 kD which belongs to thymidylate kinase family. DTYMK is important in the dTTP synthesis pathway for DNA synthesis. It participated in the pyrimidine metabolism pathway and dTTP biosynthesis pathway. DTYMK catalyzes the conversion of dTMP to dTDP and catalyzes the phosphorylation of thymidine 5'-monophosphate (dTMP) to form thymidine 5'-diphosphate (dTDP) in the presence of ATP and magnesium. 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.