Tap /Nxf1 N -Terminal Domain Mediates Homotypic Complex Assembly and Is Necessary for Nuclear RNA Export
Matzat, Leah Helen
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Permalink
https://hdl.handle.net/2142/86321
Description
Title
Tap /Nxf1 N -Terminal Domain Mediates Homotypic Complex Assembly and Is Necessary for Nuclear RNA Export
Author(s)
Matzat, Leah Helen
Issue Date
2008
Doctoral Committee Chair(s)
Lyne Levesque
Department of Study
Cell and Developmental Biology
Discipline
Cell and Developmental Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
Tap/NXF1 is the metazoan nuclear export receptor for both poly (A+) RNA as well as cellular and viral RNAs containing the constitutive transport element (CTE). Tap is a multi-domain protein that interacts directly with nucleoporin proteins of Nuclear Pore Complexes (NPCs) as well as messenger RNA cargo. It has been long understood that the NXF family is unique from the Karyopherin transport receptor family and that RNA export functions independently of the nuclear Ran-GTP gradient. Until now the mechanistic basis for Tap-mediated export has remained elusive; the work herein provides analysis of Tap homotypic complex formation and demonstrates that Tap-mediated export relies on the regulated formation of a Tap homotypic complex. Tap complex formation is mediated by the Tap N-terminal domain, the same region required for Tap-RNP interactions. To observe the functional significance of the Tap complex, constitutively monomeric mutants were generated and found to interact with the components necessary for export: nucleoporins, the export cofactor Nxt1, and RNA. Multimeric Tap is capable of forming interactions with the factors necessary for export but does not prefer binding RNA in the multimeric form, suggesting that multimeric Tap is not actively exporting cargo. Despite this apparent reliance on the Tap monomer for export, constitutively monomeric Tap mutants localize to the nucleus but lack the ability to export RNA. The requirement of the Tap complex for successful export implies that nuclear regulation of Tap complex association and dissociation is necessary prior to exit with cargo. This body of work contains a systematic characterization of the biochemical properties of the Tap protein complex, the basis for Tap complex-RNA interaction and its functional significance in vivo.
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