Transports diphosphate-N-acetylglucosamine (UDP-GlcNAc) from the cytosol into the lumen of the Golgi apparatus, functioning as an antiporter that exchanges UDP-N-acetyl-alpha-D-glucosamine for UMP (PubMed:10393322). May supply UDP-GlcNAc as substrate for Golgi- resident glycosyltransferases that generate highly branched, multiantennary complex N-glycans and keratan sulfate (PubMed:23766508, PubMed:34981577). However, the exact role of SLC35A3 still needs to be elucidated, it could be a member of a catalytically more efficient multiprotein complex rather than function independently as a single transporter (PubMed:32938718). {ECO:0000269|PubMed:10393322, ECO:0000269|PubMed:23766508, ECO:0000269|PubMed:32938718, ECO:0000269|PubMed:34981577}. This is the function of SLC35A3 (solute carrier family 35 member A3, ENSG00000117620).