Identification of a major polypeptide of the nuclear pore complex.

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Abstract
The nuclear pore complex is a prominent structural component of the nuclear envelope that appears to regulate nucleoplasmic molecular movement. None of its polypeptides were previously defined. To identify possible pore complex proteins, rat liver nuclear envelopes and microsomal membranes were fractionated with strong perturbants into peripheral and intrinsic membrane proteins, and compared these fractions on SDS [sodium dodecyl sulfate] gels. From this analysis, a prominent 190-kilodalton intrinsic membrane polypeptide occurring specifically in nuclear envelopes was identified. Lectin binding studies indicate that this polypeptide (gp 190) is the major nuclear envelope glycoprotein. Upon treatment of nuclear envelopes with Triton X-100, gp 190 remains associated with a protein substructure of the nuclear envelope consisting of pore complexes and nuclear lamina. Monospecific antibodies to gp 190 were prepared for immunocytochemical localization. Immunofluorescence staining of tissue culture cells suggest that gp 190 occurs exclusively in the nucleus during interphase. This polypeptide becomes dispersed throughout the cell in mitotic prophase when the nuclear envelope is disassembled, and subsequently returns to the nuclear surfaces during telophase when the nuclear envelope is reconstructed. Immunoferritin labeling of Triton-treated rat liver nuclei demonstrates that gp 190 occurs exclusively in the nuclear pore complex, in the regions of the cytoplasmic (and possibly nucleoplasmic) pore complex unnuli. A polypeptide that cross-reacts with gp 190 is present in diverse vertebrate species, as shown by antibody labeling of nitrocellulose SDS gel tranfers. On the basis of its biochemical characteristics, gp 190 may be involved in anchoring the pore complex to nuclear envelope membranes.