PLANT NUCLEAR-PORE COMPLEX PROTEINS ARE MODIFIED BY NOVEL OLIGOSACCHARIDES WITH TERMINAL N-ACETYLGLUCOSAMINE

Only a few nuclear pore complex (NPC) proteins, mainly in vertebrates and yeast but none in plants, have been well characterized. As an init ial step to identify plant NPC proteins, we examined whether NPC prote ins from tobacco are modified by N-acetylglucosamine (GlcNAc). Using w heat germ agglutinin, a lectin that binds specifically to GlcNAc in pl ants, specific labeling was often found associated with or adjacent to NPCs. Nuclear proteins containing GlcNAc can be partially extracted b y 0.5 M salt, as shown by a wheat germ agglutinin blot assay, and at l east eight extracted proteins were modified by terminal GlcNAc, as det ermined by in vitro galactosyltransferase assays. Sugar analysis indic ated that the plant glycans with terminal GlcNAc differ from the singl e O-linked GlcNAc of vertebrate NPC proteins in that they consist of o ligosaccharides that are larger in size than five GlcNAc residues. Mos t of these appear to be bound to proteins via a hydroxyl group. This n ovel oligosaccharide modification may convey properties to the plant N PC that are different from those of vertebrate NPCs.