May provide the missing metabolic reaction required to link the mitochondria and the cytoplasm in the mammalian model of one-carbon folate metabolism complementing thus the enzymatic activities of MTHFD2. (6S)-5,6,7,8-tetrahydrofolate + ATP + formate = (6S)-10-formyltetrahydrofolate + ADP + phosphate One-carbon metabolism; tetrahydrofolate interconversion. Homodimer. This monofunctional enzyme consists of two major domains: an N-terminal inactive methylene-THF dehydrogenase and cyclohydrolase domain and an active larger formyl-THF synthetase C-terminal domain. In the N-terminal section; belongs to the tetrahydrofolate dehydrogenase/cyclohydrolase family. In the C-terminal section; belongs to the formate--tetrahydrofolate ligase family.