It recognizes a protein of 36kDa, identified as Thymidylate Synthase (TS) (EC 18.104.22.168). It converts deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP), essential for DNA biosynthesis. TS is also a critical target for fluoropyrimidines, an essential antineoplastic drug widely used to treat solid tumors. Both 5-FU and fluorodeoxyuridine are converted in tumor cells to FdUMP, which inactivates TS by forming a ternary covalent complex in the presence of the folate cofactor 5,10-methylenetetrahydrofolate. Expression of TS protein has been reported to associate with response to 5-fluorouracil (5-FU) in human colorectal, gastric, head and neck, and breast carcinomas.