Transporter that mediates the import of reduced folates and a subset of cyclic dinucleotides. Has high affinity for N5-methyltetrahydrofolate, the predominant circulating form of folate. Also able to mediate the import of antifolate drug methotrexate. Acts as an importer of immunoreactive cyclic dinucleotides, such as cyclic GMP-AMP (2'-3'-cGAMP), an immune messenger produced in response to DNA virus in the cytosol, and its linkage isomer 3'-3'-cGAMP. Mechanistically, acts as an antiporter, which export of intracellular organic anions to facilitate uptake of its substrates. 5-amino-4-imidazolecarboxamide riboside (AICAR), when phosphorylated to AICAR monophosphate, can serve as an organic anion for antiporter activity.

> 85% as determined by SDS-PAGE.