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Cell. 1996 Oct 4;87(1):21-32.

Importin provides a link between nuclear protein import and U snRNA export.

Author information

1
Zentrum für Molekulare Biologie, Universität Heidelberg, Federal Republic of Germany.

Abstract

Importin-alpha mediates nuclear protein import by binding nuclear localization signals and importin-beta. We find approximately 30% of SRP1p, the yeast importin-alpha, in a nuclear complex with the Saccharomyces cerevisiae nuclear cap-binding protein complex (CBC). Similarly, a large fraction of Xenopus CBC is associated with importin-alpha in the nucleus. CBC promotes nuclear export of capped U snRNAs and shuttles between nucleus and cytoplasm. The CBC-importin-alpha complex binds specifically to capped RNA, suggesting that CBC might shuttle while bound to importin-alpha. Strikingly, importin-beta binding displaces the RNA from the CBC-importin-alpha complex. Thus, the commitment of CBC for nuclear reentry triggers the release of the export substrate into the cytoplasm. We provide evidence for a mechanism that ensures that importin-mediated RNA release is a specifically cytoplasmic event.

PMID:
8858145
DOI:
10.1016/s0092-8674(00)81319-7
[Indexed for MEDLINE]
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