A BIOCHEMICAL AND IMMUNOLOGICAL COMPARISON OF NUCLEAR AND CYTOPLASMICPORE COMPLEXES

Pore complexes are not confined to the nuclear envelope but can also b e found in the cytoplasm of numerous cell types in the form of annulat e lamellae (AL). We have induced formation of AL by exposure of rat ce lls (line RV) to sublethal doses of the antimitotic drug vinblastine s ulfate, and compared the distribution of several nuclear pore complex proteins (nucleoporins) in the nuclear envelope and AL by immunocytoch emistry, cytochemical lectin binding studies and immunoblot analyses o f nuclear and AL-enriched fractions. All the antibodies used yielded p unctate nuclear surface staining in immunofluorescence microscopy whic h is characteristic for nuclear pore complex components. When we appli ed antibodies against the nucleoporin p62, AL were visualized as numer ous cytoplasmic dot-like structures. Immunogold electron microscopy co nfirmed the correspondence of the cytoplasmic bodies with stacks of AL . Antibodies to constituents of the cytoplasmic (nupl80) and nucleopla smic (nup153) filaments extending from both sides of nuclear pore comp lexes also stained the AL, indicating that pore complexes are intrinsi cally asymmetric assemblies independent of their specific intracellula r topology. By contrast, AL were negative with five different antibodi es against the transmembrane nuclear pose glycoprotein gp210 and the l ectin concanavalin A (ConA) known to bind to the oligosaccharide side chains of gp210. Similarly, there was no staining of the AL with antib odies to the other nuclear pore membrane protein so far known in highe r eukaryotes, POM121. Immunoblot analyses confirmed the presence of p6 2, nup180 and nup153 in both the nuclear and AL fractions and the abse nce of gp210 and POM121 from AL. Our results do not support the genera lly held view that gp210 and POM121 function in anchoring the pore com plex scaffold to the pore membrane. Rather, they point to a role for t hese proteins in transport processes through the nuclear pore complexe s, Since AL are not involved in nucleocytoplasmic transport processes they may lack components of the transport machinery.