Transports both UDP-glucuronic acid (UDP-GlcA) and UDP-N-acetylgalactosamine (UDP-GalNAc) from the cytoplasm into the endoplasmic reticulum lumen (PubMed:11322953, PubMed:17952091). Plays a role in chondroitin sulfate biosynthesis, which is important for formation of cartilage extracellular matrix and normal skeletal development (By similarity). Ubiquitous. The disease is caused by variants affecting the gene represented in this entry. Belongs to the TPT transporter family. SLC35D subfamily. Extended N-terminus.