AN ANTIBODY AGAINST A GLYCOSYLATED INTEGRAL MEMBRANE-PROTEIN OF THE XENOPUS-LAEVIS NUCLEAR-PORE COMPLEX - A TOOL FOR THE STUDY OF PORE COMPLEX MEMBRANES

We have recently described a monoclonal antibody (X222) which localize s at pore complexes in Xenopus oocytes and immunoblots a protein under nonreducing renditions with an apparent molecular mass of 215 kDa (Co rdes, Gajewski, Stumpp, Krohne, Differentiation 58, 307-312, (1995)), Under reducing renditions, this antigen decreased from the previously reported 215 kDa to 200 kDa. Since this protein binds to the lectin co ncanavalin A (Con A), we now refer to it as gp200. In addition to Con A binding, Xenopus gp200 has several other Features in common with the mammalian pore membrane protein gp210. On nuclear envelopes extracted with Triton X-100, gp200 was localized on the lateral wails of pores, a subdomain revered in native nuclear envelopes by the lipid bilayer. In mitotic extracts of Xenopus eggs gp200 was exclusively, recovered in the membrane fraction, Treatment of oocyte membranes with urea and proteases indicated that gp200 is an integral membrane protein with th e bulk of its mass located within the membrane lumen, In Xenopus oocyt e nuclei gp200 is the major Con A binding protein, The new monoclonal antibody X222 has allowed us to characterize the first integral membra ne protein, gp200, of the Xenopus pore complex.