A novel second isoenzyme of the human UDP-N-acetylglucosamine :alpha 1,3-D-mannoside beta 1,4-N-acetylglucosaminyltransferase family: cDNA cloning, expression, and chromosomal assignment

We isolated a novel cDNA encoding a second isoenzyme of UDP-N-acetylglucosa mine:alpha 1,3-D-mannoside beta 1,4-N-acetylglucosaminyltransferase (GnT-IV ; EC 2.4.1.145). The nucleotide and deduced amino acid sequences of the cDN A were homologous to those of the previously cloned human GnT-IV cDNA (63% and 62% identity, respectively). The new cDNA is also confirmed to express GnT-IV activity, suggesting that two isoenzymes of human GnT-IV exist. Alth ough genomic Southern analysis suggested that both genes exist in many mamm alian species and the chicken, northern analysis revealed that both genes a re expressed in different ways in human tissues. This is the first report c oncerning the gene family of an N-acetylglucosaminyltransferase in mammals.