The de novo thymidylate synthesis pathway as a nuclear multienzyme complex at sites of DNA replication. THF, tetrahydrofolate; DHF, dihydrofolate; MTHFD1, Methylenetetrahydrofolate Dehydrogenase; SHMT1, Cytoplasmic Serine Hydroxymethyltransferase; TYMS, Thymidylate Synthase; DHFR, Dihydrofolate Reductase; dUMP, deoxyuridine monophosphate; dUTP, deoxyuridine triphosphate; dTMP, thymidine monophosphate; dTTP, thymidine triphosphate.