β-1,4-Gal-T1 Background Information The ∫-1,4-Gal-T1 gene, which maps to chromosome 9p13, is one of seven beta-1,4-galactosyltransferase (∫-1,4-Gal-T) genes (1,2). These genes encode type II membrane-bound glycoproteins that appear to have exclusive specificity for the donor substrate UDP-galactose (2,3). These protein products transfer galactose in a beta1,4 linkage to similar acceptor sugars, such as GlcNAc, Glc, and Xyl (4). These type II membrane glycoproteins have an N-terminal hydrophobic signal sequence that directs the protein to the Golgi apparatus and remains uncleaved to function as a transmembrane anchor (5). The ∫-1,4-Gal-T1 gene is unique among the ∫-1,4-Gal-T genes in that it encodes an enzyme that participates in both glycoconjugation and lactose biosynthesis(6). The ∫-1,4-Gal-T1 protein is encoded by two transcripts with approximate lengths of 4.1 kb and 3.9 kb, which differ only at their 5' ends (4). The longer transcript encodes the type II membrane-bound, trans-Golgi resident protein involved in glycoconjugate biosynthesis (4). The shorter transcript encodes a protein that is cleaved to form the soluble lactose synthase (4,6).
