The function of SLC35A1 (solute carrier family 35 member A1, ENSG00000164414) is as follows. Transports CMP-sialic acid from the cytosol into the Golgi apparatus, functioning as an antiporter that exchanges CMP-sialic acid for CMP (PubMed:12682060, PubMed:15576474, PubMed:23873973). Binds both CMP-sialic acid and free CMP, but has higher affinity for free CMP (By similarity). Also able to exchange CMP-sialic acid for AMP and UMP (PubMed:12682060). Also mediates the transport of CDP-ribitol (By similarity). {ECO:0000250|UniProtKB:Q61420, ECO:0000269|PubMed:12682060, ECO:0000269|PubMed:15576474, ECO:0000269|PubMed:23873973}.