INSERTION INTO ASPERGILLUS-NIDULANS OF FUNCTIONAL UDP-GLCNAC - ALPHA-3-D-MANNOSIDE BETA-1,2-N-ACETYLGLUCOSAMINYL-TRANSFERASE-I, THE ENZYME CATALYZING THE FIRST COMMITTED STEP FROM OLIGOMANNOSE TO HYBRID AND COMPLEX N-GLYCANS

Filamentous fungi are capable of secreting relatively large amounts of heterologous recombinant proteins. Recombinant human glycoproteins expressed in this system, however, carry only carbohydrates of the oligomannose type limiting their potential use in humans. One approach to the problem is genetic engineering of the fungal host to permit production of comp lex and hybrid N-glycans. UDP-GlcNAc: alpha 3-D-mannoside beta 1,2-N-acetylglucosaminyltransferase I (GnT I) is essential for the conversion of oligomannose to hybrid and complex N-glycans in higher eukaryotic cells. Since GnT I is not produced by fungi, we have introduced into the genome of Aspergillus nidulans the gene encoding full-length rabbit GnT I and demonstrated the expression of GnT I enzyme activity at levels appreciably higher than occurs in most mammalian tissues. All the GnT I activity in the Aspergillus transformants remains intracellular suggesting that the rabbit trans-membrane sequence may be capable of targeting GnT I to the fungal Golgi apparatus.