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Division of Cell Biology, German Cancer Research Center, D-69120 Heidelberg, Federal Republic of Germany
Using a monoclonal antibody, mAb 203-37, we have identified a polypeptide of Mr ~270 kD (p270)
as a general constituent of the intranuclear filaments attached to the nucleoplasmic annulus of the nuclear
pore complex (NPC) in diverse kinds of vertebrate cells. Using cDNA cloning and immunobiochemistry,
we show that human protein p270 has a predicted molecular mass of 267 kD and is essentially identical to the
coiled-coil dominated protein Tpr reported by others to
be located on the outer, i.e., cytoplasmic surface of
NPCs (Byrd, D.A., D.J. Sweet, N. Pante, K.N. Konstantinov, T. Guan, A.C.S. Saphire, P.J. Mitchell, C.S. Cooper, U. Aebi, and L. Gerace. 1994. J. Cell Biol. 127:
1515-1526). To clarify this controversial localization,
we have performed immunoelectron microscopy in diverse kinds of mammalian and amphibian cells with a
series of antibodies raised against different epitopes of
human and Xenopus laevis p270/Tpr. In these experiments, the protein has been consistently and exclusively
detected in the NPC-attached intranuclear filaments,
and p270/Tpr-containing filament bundles have been
traced into the nuclear interior for up to 350 nm. No reaction has been noted at the cytoplasmic side of NPCs
with any of the p270/Tpr antibodies, whereas control
antibodies such as those against protein RanBP2/
Nup358 specifically decorate the cytoplasmic annulus
of NPCs. Pore complexes of cytoplasmic annulate lamellae in various mammalian and amphibian cells are
also devoid of immunodetectable protein p270/Tpr. We
conclude that this coiled-coil protein is a general and
ubiquitous component of the intranuclear NPC-
attached filaments and discuss its possible functions.
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