The yeast nucleoporin Nup53p specifically interacts with Nic96p and is directly involved in nuclear protein import

The bidirectional nucleocytoplasmic transport of macromolecules is mediated by the nuclear pore complex (NPC) which, in yeast, is composed of similar to 30 different proteins (nucleoporins). Preembedding immunogold-electron m icroscopy revealed that Nic96p, an essential yeast nucleoporin, is located about the cytoplasmic and the nuclear periphery of the central channel, and near or at the distal ring of the yeast NPC. Genetic approaches further im plicated Nic96p in nuclear protein import. To more specifically explore the potential role of Nic96p in nuclear protein import, we performed a two-hyb rid screen with NIC96 as the bait against a yeast genomic library to identi fy transport factors and/or nucleoporins involved in nuclear protein import interacting with Nic96p. By doing so, we identified the yeast nucleoporin Nup53p, which also exhibits multiple locations within the yeast NPC and col ocalizes with Nic96p in all its locations. Whereas Nup53p is directly invol ved in NLS-mediated protein import by its interaction with the yeast nuclea r import receptor Kap95p, it arrears not to participate in NES-dependent nu clear export.