Sugar transporter that specifically mediates the transport of UDP-N-acetylglucosamine (UDP-GlcNAc), GDP-fucose and UDP-xylose. Functions redundantly with nac in the O-fucosylation of Notch, positively regulating Notch signaling. Involved in the biosynthesis of heparan sulfate-glycosaminoglycan (HS-GAG) and in Dpp signaling in the wing imaginal disk. Expressed maternally and zygotically. Homozygous lethal. In a weak loss-of-function phenotype, a gap in the fifth longitudinal vein of the adult wing is observed. Belongs to the nucleotide-sugar transporter family. SLC35B subfamily.