Mutations in tap uncouple RNA export activity from translocation through the nuclear pore complex.
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.
Lévesque
Lyne
L
Department of Cell and Developmental Biology, University of Illinois in Urbana-Champaign, Urbana, IL 61801, USA. levesque@uiuc.edu
Bor
Yeou-Cherng
YC
Matzat
Leah H
LH
Jin
Li
L
Berberoglu
Stephen
S
Rekosh
David
D
Hammarskjöld
Marie-Louise
ML
Paschal
Bryce M
BM
D018528:ATP-Binding Cassette Transporters; D021581:Active Transport, Cell Nucleus; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002459:Cell Fusion; D002522:Chlorocebus aethiops; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D006801:Humans; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D022022:Nuclear Pore / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D034443:RNA Transport; D012333:RNA, Messenger / Q000378:metabolism*
D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; C498546:NXT1 protein, human; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; C477327:transporter associated with antigen processing (TAP)