A Family of Human β3-Galactosyltransferases

BLAST analysis of expressed sequence tags (ESTs) using the coding sequence of a human UDP-galactose:β-N-acetyl-glucosamine β-1,3-galactosyltransferase, designated β3Gal-T1, revealed no ESTs with identical sequences but a large number with similarity. Three different sets of overlapping ESTs with sequence similarities to β3Gal-T1 were compiled, and complete coding regions of these genes were obtained. Expression of two of these genes in the Baculo virus system showed that one represented a UDP-galactose:β-N-acetyl-glucosamine β-1,3-galactosyltransferase (β3Gal-T2) with similar kinetic properties as β3Gal-T1. Another gene represented a UDP-galactose:β-N-acetyl-galactosamine β-1,3-galactosyltransferase (β3Gal-T4) involved in GM1/GD1 ganglioside synthesis, and this gene was highly similar to a recently reported rat GD1 synthase (Miyazaki, H., Fukumoto, S., Okada, M., Hasegawa, T., and Furukawa, K. (1997) J. Biol. Chem. 272, 24794–24799). Northern analysis of mRNA from human organs with the four homologous cDNA revealed different expression patterns. β3Gal-T1 mRNA was expressed in brain, β3Gal-T2 was expressed in brain and heart, and β3Gal-T3 and -T4 were more widely expressed. The coding regions for each of the four genes were contained in single exons. β3Gal-T2, -T3, and -T4 were localized to 1q31, 3q25, and 6p21.3, respectively, by EST mapping. The results demonstrate the existence of a family of homologous β3-galactosyltransferase genes.