A Karyophilic Protein Forms a Stable Complex with Cytoplasmic Components Prior to Nuclear Pore Binding (*)
- From the (1) Department of Anatomy and Cell Biology, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka 565, Japan
- § To whom correspondence should be addressed. Tel.: 81-6-879-3211; Fax: 81-6-879-3219.
Abstract
Targeting of karyophilic proteins to nuclear pores is known to require several cytoplasmic factors, including the nuclear location signal-binding protein. Using a digitonin-permeabilized cell-free transport assay, we have obtained a cytoplasmic fraction containing factors that specifically bind to karyophilic protein and support the nuclear binding step of the transport. Components in this fraction form a stable complex with the karyophile through interaction with nuclear location signal. Since this complex shows nuclear pore binding activity prior to nuclear entry in the absence of other cytosolic factors, we call it nuclear pore-targeting complex. It consists of karyophilic protein and four proteins of 54, 56, 66, and 90 kDa. In our reconstitution experiments, a complex with 54 and 90 kDa proteins is capable of targeting karyophiles to the nuclear pores.
Footnotes
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↵* This work was supported by grants from the Japanese Ministry of Education, Science and Culture and the Nissan Science Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- NLS
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nuclear location signal
- WGA
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wheat germ agglutinin
- APC
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allophycocyanin
- bBSA
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biotinylated bovine serum albumin
- hsc70
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70-kDa heat-shock cognate protein
- Ran/TC4
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Ras-related nuclear protein.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
