Glycosyltransferase that initiates the elongation of O-linked fucose residues attached to EGF-like repeats in the extracellular domain of Notch molecules. 3-O-(alpha-L-fucosyl)-L-threonyl-[EGF-like domain protein] + UDP-N-acetyl-alpha-D-glucosamine = 3-O-(N-acetyl-beta-D-glucosaminyl-(1->3)-alpha-L-fucosyl)-L-threonyl-[EGF-like domain protein] + H(+) + UDP 3-O-(alpha-L-fucosyl)-L-seryl-[EGF-like domain protein] + UDP-N-acetyl-alpha-D-glucosamine = 3-O-(N-acetyl-beta-D-glucosaminyl-(1->3)-alpha-L-fucosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP First detected at the 12-somite stage. From the 20-somite stage, expressed in the otic vesicle. Belongs to the glycosyltransferase 31 family.