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Vol. 17, Issue 2, 931-943, February 2006

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Mutations in Tap Uncouple RNA Export Activity from Translocation through the Nuclear Pore Complex

Lyne Lévesque ^*, Yeou-Cherng Bor , Leah H. Matzat ^*, Li Jin , Stephen Berberoglu ^*, David Rekosh , Marie-Louise Hammarskjöld , and Bryce M. Paschal 

^* Department of Cell and Developmental Biology, University of Illinois in Urbana-Champaign, Urbana, IL 61801; Myles H. Thaler Center for AIDS and Human Retrovirus Research and Department of Microbiology, University of Virginia, Charlottesville, VA 22908-0577; and Center for Cell Signaling, Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908-0577

Submitted July 27, 2004; Revised November 9, 2005; Accepted November 16, 2005
Monitoring Editor: Sandra Schmid

Interactions between transport receptors and phenylalanine-glycine (FG) repeats on nucleoporins drive the translocation of receptor-cargo complexes through nuclear pores. Tap, a transport receptor that mediates nuclear export of cellular mRNAs, contains a UBA-like and NTF2-like folds that can associate directly with FG repeats. In addition, two nuclear export sequences (NESs) within the NTF2-like region can also interact with nucleoporins. The Tap-RNA complex was shown to bind to three nucleoporins, Nup98, p62, and RanBP2, and these interactions were enhanced by Nxt1. Mutations in the Tap-UBA region abolished interactions with all three nucleoporins, whereas the effect of point mutations within the NTF2-like domain of Tap known to disrupt Nxt1 binding or nucleoporin binding were nucleoporin dependent. A mutation in any of these Tap domains was sufficient to reduce RNA export but was not sufficient to disrupt Tap interaction with the NPC in vivo or its nucleocytoplasmic shuttling. However, shuttling activity was reduced or abolished by combined mutations within the UBA and either the Nxt1-binding domain or NESs. These data suggest that Tap requires both the UBA- and NTF2-like domains to mediate the export of RNA cargo, but can move through the pores independently of these domains when free of RNA cargo.

Address correspondence to: Lyne Lévesque (levesque{at}uiuc.edu).

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