A specific glycosyltransferase is required for the synthesis of each of the different disaccharide linkages that are known to be present in the oligosaccharide moieties of glycoproteins and glycolipids, which are referred to as glycoconjugates. Galactosyltransferases, a subgroup of the transferases, constitute a family of enzymes which transfer galactose from UDP-gal to the non-reducing residues of oligosaccharides of various glycoconjugates as well as to monosaccharides. We have initiated the molecular cloning approach to understand the modulation of the galactosyltransferase activity, essential for generating specific cell-surface antigenic determinants. In our previous studies on the gene structural analyses of alpha-lactalbumin, a modifier or a specifier protein of galactosyltransferase, we showed that the domain of alpha-lactalbumin that interacts with galactosyltransferase is coded entirely by a separate exon. In the present studies we have cloned and sequenced a cDNA of bovine N-acetyl glucosamine Beta1-4galactosyltransferase and addressed the question of whether the family of galactosyltransferases have common structural and sequence features despite their varying specificities. Several sequence-related cDNA clones were isolated. cDNA insert of one set of clones encodes a protein sequence that includes the amino acid sequences of five peptides of bovine galactosyltransferase. The in vitro-translated products coded by human mRNA hybrid-selected with these sets of clones were immunologically reactive with monoclonal antibodies that recognized human but not the bovine 1-4galactosyltransferase epitopes. The sequence analyses of the cDNA clones from several sets show that the regions of the mRNA coding for either carboxylterminal or other domains of the protein are identical with other cDNA clones which may code for proteins that are structurally and may be functionally related to other galactosyl or galactosyltransferases.
