Antiporter that mediates the import of reduced folates or a subset of cyclic dinucleotides, driven by the export of organic anions (PubMed:7826387, PubMed:9041240, PubMed:10787414, PubMed:15337749, PubMed:16115875, PubMed:22554803, PubMed:31511694, PubMed:31126740, PubMed:32276275). Mechanistically, acts as a secondary active transporter, which exports intracellular organic anions down their concentration gradients to facilitate the uptake of its substrates (PubMed:22554803, PubMed:31511694, PubMed:31126740). Has high affinity for N5-methyltetrahydrofolate, the predominant circulating form of folate (PubMed:10787414, PubMed:14609557, PubMed:22554803). Also able to mediate the import of antifolate drug methotrexate (PubMed:7615551, PubMed:7641195, PubMed:9767079, PubMed:22554803). Also 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, thus playing a role in triggering larger immune responses (PubMed:31511694, PubMed:31126740). 5-amino-4-imidazolecarboxamide riboside (AICAR), when phosphorylated to AICAR monophosphate, can serve as an organic anion for antiporter activity (PubMed:22554803). (6S)-5-methyl-5,6,7,8-tetrahydrofolate(out) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(in) = (6S)-5-methyl-5,6,7,8-tetrahydrofolate(in) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(out) 2',3'-cGAMP(out) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(in) = 2',3'-cGAMP(in) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(out) 3',3'-cGAMP(out) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(in) = 3',3'-cGAMP(in) + 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide(out) Placenta, liver, and to a much smaller extent, in lung. The disease is caused by variants affecting the gene represented in this entry. Belongs to the reduced folate carrier (RFC) transporter (TC 2.A.48) family.