N-Acetyllactosaminide β-1,3-N-Acetylglucosaminyltransferase (B3GNT1) is a member of the β-1,3-N-Acetylglucosaminyltransferase family. B3GNT1 is a single-pass type II membrane protein and widely expressed in many tissues. B3GNT1 can initiate the synthesis or the elongation of the linear poly-N-acetyllactosaminoglycans. B3GNT1 is essential for the synthesis of poly-N-acetyllactosamine, a determinant for the blood group i antigen. It can initiate the synthesis or the elongation of the linear poly-N-acetyllactosaminoglycans.