The function of TYMS (thymidylate synthetase, Ensembl gene identifier ENSG00000176890) is as follows. Catalyzes the reductive methylation of 2'-deoxyuridine 5'- monophosphate (dUMP) to thymidine 5'-monophosphate (dTMP), using the cosubstrate, 5,10- methylenetetrahydrofolate (CH2H4folate) as a 1- carbon donor and reductant and contributes to the mitochondrial and nuclear de novo thymidylate biosynthesis pathway. {ECO:0000269|PubMed:11278511, ECO:0000269|PubMed:21876188, ECO:0000269|PubMed:22235121}.