the "mthfd2l" gene consists of nine exons and is conserved among mammals. this gene encodes a 340-residue protein that is homologous to the mitochondrial bifunctional dehydrogenase/cyclohydrolase (mthfd2) and to the n-terminal dehydrogenase/cyclohydrolase domains of cytoplasmic and mitochondrial c1-thf synthases (mthfd1 and mthfd1l, respectively). the mthfd2l protein contains a predicted n-terminal mitochondrial targeting sequence and four amino acids (lys-93, arg-206, gly-211, and arg-238) necessary for the protein's dehydrogenase/cyclohydrolase activity. three classes of mthfd2l rna transcripts have been detected at equal levels in adult human brain and placenta, though their translation into stable proteins in vivo has not been confirmed.