cDNA cloning, expression, and chromosomal localization of human N-acetylglucosaminyltransferase III (GnT-III)

UDP-N-acetylglucosamine:beta-D-mannoside beta 1,4 N-acetylglucosaminyltransferase III (GnT-III) [EC 2.4.1.144] catalyzes the addition of N-acetylglucosamine in beta 1-4 linkage to the beta-linked mannose of the trimannosyl core of N-linked sugar chains to produce a bisecting GlcNAc residue. We have isolated six independent cDNA clones of human GnT-III from a fetal liver cDNA library. The cDNA sequence has an open reading frame that predicts a protein of 531 amino acids. The homology to rat GnT-III is 86% at the nucleotide level and is 91% at the amino acid level. The amino-terminal transmembrane domain and the catalytic domain are well conserved in the two species. Human GnT-III has a deletion of four amino acids in the "neck" region and several differences in the COOH-terminal region compared with the rat sequence. Using one of the human cDNA clones as the probe, two overlapping genomic clones have been isolated from a human cosmid library. The GnT-III gene has been mapped to chromosome 22q.13.1 using fluorescence in situ hybridization.