胸苷酸合成酶利用5,10-亞甲基四氫葉酸（亞甲基四氫葉酸）作為輔因子催化脫氧尿苷酸甲基化為脫氧胸苷酸。此功能維持DNA復制和修復的關鍵DTMP（胸腺嘧啶-5-一磷酸素）池。這種酶作為腫瘤化療藥物的靶點一直備受關注。它被認為是5-氟尿嘧啶、5-氟尿嘧啶-2-原脫氧尿苷和一些葉酸類似物的主要作用部位。該基因和自然產生的反義轉錄本rtsalpha（geneid:55556）的表達在細胞生長從晚期對數階段向平穩期呈負向變化。
Thymidylate synthase catalyzes the methylation of deoxyuridylate to deoxythymidylate using 5,10-methylenetetrahydrofolate (methylene-THF) as a cofactor. This function maintains the dTMP (thymidine-5-prime monophosphate) pool critical for DNA replication and repair. The enzyme has been of interest as a target for cancer chemotherapeutic agents. It is considered to be the primary site of action for 5-fluorouracil, 5-fluoro-2-prime-deoxyuridine, and some folate analogs. Expression of this gene and that of a naturally occuring antisense transcript rTSalpha (GeneID:55556) vary inversely when cell-growth progresses from late-log to plateau phase.