ANALYSES OF THE CDNA CLONES FOR BETA 1-4 GALACTOSYLTRASFERASE

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A specific glycosyltransferase is required for the synthesis of oligosaccharide moieties of glycoproteins and glycolipids, which are referred to as glycoconjugates. Galactsyltransferases (gal- transf), a subgroup of the transferases, constitute a family of enzymes which transfer galatose 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 gal-transf activity, essential for generating specific cell-surface antigenic determinants. In our previous studies on the gene structural analyses of alpha-lactalbumin, a modifier protein of gal-transf, we showed that the domain of alpha-lactalbumin that interacts with gal-transf is coded entirely by a separate exon. We have now cloned and sequenced cDNA coding for bovine GlcNAc 1-4 gal-transf. Analysis of several sequence-related cDNA clones showed: 1) There are at least two chromosomal sequences for 1- 4 gal-transf; 2) There are two major classes of mRNAs which share common nucleotide sequences encoding the proteins with the same carboxy-terminal end of 120 residues and share same 3' noncoding sequence. One class of clones encode 1-4 gal-transf protein sequence; 3) The enzyme must be synthesized as a proprotein and secreted as cleaved product which is enzymatically active; 4) Series of poly(A) sites present in the gene sequence are utilized to generate mRNAs of different sizes which vary in length at the 3' non-coding region; 5) The cDNA clones which have different nucleotide sequence at the 5' end compared to the clones coding for the 1-4 gal-transf, do not encode any protein sequence in any of the three open reading frames suggesting that they may represent unspliced precursor mRNAs; 6) The nucleotide sequence analysis of several related cDNA clones suggest that a complex alternative processing of the precursor mRNA occurs to generate gal-transf mRNAs.