Genomic cloning and expression of three murine UDP-galactose:: β-N-acetylglucosamine β1,3-galactosyltransferase genes

Based on the detection of expressed sequence tags that are similar to known galactosyltransferase sequences, we have isolated three novel UDP-galactose:beta-N-acetylglucosamine beta 1,3-galactosyltransferase (beta 3GalT) genes from a mouse genomic library, The three genes, named beta 3GalT-I, -II, and -III, encode type II transmembrane proteins of 326, 422, and 331 amino acids, respectively, The three proteins constitute a distinct subfamily as they do not share any sequence identity with other eucaryotic galactosyltransferases. Also, the entire protein-coding region of the three beta 3GalT genes was contained in a single exon, which contrasts with the genomic organization of the beta 1,4 and alpha 1,3-galactosyltransferase genes, The three beta 3GalT genes were mainly expressed in brain tissue, The expression of the full-length murine genes as recombinant baculoviruses in insect cells revealed that the beta 3GalT enzymes share the same acceptor specificity for beta-linked GlcNAc, although they differ in their K-m for this acceptor and the donor UDP-Gal. The identification of beta 3GalT genes emphasizes the structural diversity present in the galactosyltransferase gene family.