RNA



The C-terminal domain of TAP interacts with the nuclear pore complex and promotes export of specific CTE-bearing RNA substrates


ANGELA  BACHI a1 1 , ISABELLE C.  BRAUN a2 1 p1, JOÃO P.  RODRIGUES a3 1 , NELLY  PANTÉ a4 1 , KATHARINA  RIBBECK a5, CAYETANO  VON KOBBE a2, ULRIKE  KUTAY a5, MATTHIAS  WILM a1, DIRK  GÖRLICH a5, MARIA  CARMO-FONSECA a3 and ELISA  IZAURRALDE a2p1c1
a1 European Molecular Biology Laboratory, D-69117 Heidelberg, Germany
a2 University of Geneva, Department of Molecular Biology, CH-1205 Geneva, Switzerland
a3 Institute of Histology and Embryology, Faculty of Medicine, University of Lisbon, 1699 Lisboa Codex, Portugal
a4 Institute of Biochemistry, Swiss Federal Institute of Technology (ETH), CH-8092 Zürich, Switzerland
a5 Zentrum für Molekulare Biologie der Universität Heidelberg, 69120 Heidelberg, Germany

Abstract

Messenger RNAs are exported from the nucleus as large ribonucleoprotein complexes (mRNPs). To date, proteins implicated in this process include TAP/Mex67p and RAE1/Gle2p and are distinct from the nuclear transport receptors of the [beta]-related, Ran-binding protein family. Mex67p is essential for mRNA export in yeast. Its vertebrate homolog TAP has been implicated in the export of cellular mRNAs and of simian type D viral RNAs bearing the constitutive transport element (CTE). Here we show that TAP is predominantly localized in the nucleoplasm and at both the nucleoplasmic and cytoplasmic faces of the nuclear pore complex (NPC). TAP interacts with multiple components of the NPC including the nucleoporins CAN, Nup98, Nup153, p62, and with three major NPC subcomplexes. The nucleoporin-binding domain of TAP comprises residues 508–619. In HeLa cells, this domain is necessary and sufficient to target GFP-TAP fusions to the nuclear rim. Moreover, the isolated domain strongly competes multiple export pathways in vivo, probably by blocking binding sites on the NPC that are shared with other transport receptors. Microinjection experiments implicate this domain in the export of specific CTE-containing RNAs. Finally, we show that TAP interacts with transportin and with two proteins implicated in the export of cellular mRNAs: RAE1/hGle2 and E1B-AP5. The interaction of TAP with nucleoporins, its direct binding to the CTE RNA, and its association with two mRNP binding proteins suggest that TAP is an RNA export mediator that may bridge the interaction between specific RNP export substrates and the NPC.

(Received September 9 1999)
(Revised October 19 1999)
(Accepted October 27 1999)


Key Words: CTE; mRNA export; nucleoporins; nuclear export; TAP.

Correspondence:
c1 Reprint requests to: Elisa Izaurralde, European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany; e-mail: izaurralde@embl-heidelberg.de.
p1 Present address: European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.


Footnotes

1 These authors contributed equally to this work.