Homocysteine metabolism in yeast. The following abbreviations are used: STR4, cystathionine β-synthase homolog in yeast; SAH1, S-adenosyl-l-homocysteine hydrolase; MET6, methionine synthase; CDC21, thymidylate synthase; MET13, methylenetetrahydrofolate reductase; SHM2, serine hydroxymethyltransferase; dUMP, deoxyuridine 5-monophosphate; dTMP, deoxythymidine 5′-monophosphate; SAM1, SAM2, S-adenosylmethionine synthetase; MHT1, S-methylmethionine-homocysteine methyltransferase; THF, tetrahydrofolate; SAM, AdoMet; SAH, AdoHcy.