title: Formation of Tap/NXT1 heterodimers activates Tap-dependent nuclear mRNA export by enhancing recruitment to nuclear pore complexes.
abstract: The Tap protein has been shown to activate the nuclear export of mRNA species bearing retroviral constitutive transport elements and is also believed to play an essential role in the sequence nonspecific export of cellular mRNAs. However, it has remained unclear how Tap activity is regulated in vivo. Here, we report that the small NXT1/p15-1 protein functions as a critical cofactor for Tap-mediated mRNA export in both human and invertebrate cells. In the absence of NXT1 binding, the Tap protein is unable to effectively interact with components of the nuclear pore complex and both Tap nucleocytoplasmic shuttling and the nuclear export of mRNA molecules tethered to Tap are therefore severely attenuated. Formation of a Tap/NXT1 heterodimer enhances nucleoporin binding both in vitro and in vivo and induces the formation of a Tap/NXT1/nucleoporin ternary complex that is likely to be a key intermediate in the process of nuclear mRNA export. The critical importance of NXT1 for the nuclear export of poly(A)(+) RNA is emphasized by the finding that specific inhibition of the expression of the Drosophila homolog of human NXT1, by using RNA interference, results in the nuclear accumulation of poly(A)(+) RNA in cultured insect cells. These data suggest that NXT1 may act as a molecular switch that regulates the ability of Tap to mediate nuclear mRNA export by controlling the interaction of Tap with components of the nuclear pore.
authors.affiliation: Howard Hughes Medical Institute and Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Heather L
authors.initials: HL
authors.lastname: Wiegand
authors.forename: Glen A
authors.initials: GA
authors.lastname: Coburn
authors.forename: Yan
authors.initials: Y
authors.lastname: Zeng
authors.forename: Yibin
authors.initials: Y
authors.lastname: Kang
authors.forename: Hal P
authors.initials: HP
authors.lastname: Bogerd
authors.forename: Bryan R
authors.initials: BR
authors.lastname: Cullen
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D004330:Drosophila; D029721:Drosophila Proteins; D005456:Fluorescent Dyes / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D022022:Nuclear Pore / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019713:Receptors, CCR5 / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D000097606:Exportin 1 Protein
chemical_list: D002352:Carrier Proteins; D029721:Drosophila Proteins; D005456:Fluorescent Dyes; D028884:Karyopherins; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D019713:Receptors, CCR5; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D000097606:Exportin 1 Protein; C122111:NXF1 protein, human; C498546:NXT1 protein, human; C498545:Nxt1 protein, Drosophila