Thymidylate synthase catalyzes the methylation of deoxyuridylate to deoxythymidylate using 5，10-methylenetetrahydrofolate as a cofactor which maintains the dTMP（thymidine-5-prime monophosphate) pool vital for DNA replication and repair. Thymidylate synthase plays an important role as a cancer chemotherapeutic agent. Thymidylate synthase is the primary site of action for 5-fluorouracil， 5-fluoro-2-prime-deoxyuridine， and several folate analogs.
