CDNA CLONING, EXPRESSION, AND CHROMOSOMAL LOCALIZATION OF HUMAN N-ACETYLGLUCOSAMINYLTRANSFERASE-III (GNT-III)

UDP-N-acetylglucosamine: beta-D-mannoside beta1,4 N-acetylglucosaminyl transferase III (GnT-III) [EC 2.4.1.144] catalyzes the addition of N-a cetylglucosamine in beta1-4 linkage to the beta-linked mannose of the trimannosyl core of N-linked sugar chains to produce a bisecting GlcNA c residue. We have isolated six independent cDNA clones of human GnT-I II from a fetal liver cDNA library. The cDNA sequence has an open read ing 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 aci d level. The amino-terminal transmembrane domain and the catalytic dom ain are well conserved in the two species. Human GnT-III has a deletio n of four amino acids in the ''neck'' region and several differences i n the COOH-terminal region compared with the rat sequence. Using one o f the human cDNA clones as the probe, two overlapping genomic clones h ave been isolated from a human cosmid library. The GnT-III gene has be en mapped to chromosome 22q.13.1 using fluorescence in situ hybridizat ion.