Transports nucleotide sugars from the cytosol into Golgi vesicles where glycosyltransferases function. Interacts with SLC35A3; the interaction is reduced in the presence of SLC35A4 (PubMed:23089177, PubMed:28167211). Found in a complex with SLC35A3 and SLC35A4 (PubMed:28167211). Interacts with B4GALT4. The disease is caused by variants affecting the gene represented in this entry. Belongs to the nucleotide-sugar transporter family. SLC35A subfamily.