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The importin-ß P446L dominant-negative mutant protein loses RanGTP binding ability and blocks the formation of intact nuclear envelope

Gyula Timinszky^1,*, László Tirián^1,*, Ferenc T. Nagy^1,4, Gábor Tóth², András Perczel³, Zsuzsanna Kiss-László¹, Imre Boros⁴, Paul R. Clarke⁵ and János Szabad^1,

¹ The University of Szeged, Faculty of Medicine, Department of Biology, Somogyi B. u. 4, H-6720 Szeged, Hungary
² The University of Szeged, Faculty of Medicine, Department of Chemistry, Szeged, Hungary
³ Department of Organic Chemistry, Eötvös Loránd University, Budapest, Hungary
⁴ Biological Research Center of the Hungarian Academy of Sciences, Szeged, Temesvári krt. 62, H-6720, Hungary
⁵ Biomedical Research Center, University of Dundee, Level 5, Ninewells Hospital and Medical School, Dundee, DD1 9SY, UK
^* These authors contributed equally to this work

Author for correspondence (e-mail: szabad{at}comser.szote.u-szeged.hu )

Accepted 13 January 2002

Three of the four independently induced Ketel^D dominantnegative female sterile mutations that identify the Drosophila importin-ß gene, originated from a C4114 T transition and the concurrent replacement of Pro446 by Leu (P446L). CD spectroscopy of representative peptides with Pro or Leu in the crucial position revealed that upon the ProLeu exchange the P446L mutant protein loses flexibility and attains most likely an open conformation. The P446L mutation abolishes RanGTP binding of the P446L mutant form of importin-ß protein and results in increased RanGDP binding ability. Notably, the P446L mutant importin-ß does not exert its dominant-negative effect on nuclear protein import and has no effect on mitotic spindle-related functions and chromosome segregation. However, it interferes with nuclear envelope formation during mitosis-to-interphase transition, revealing a novel function of importin-ß.

Key words: Importin-ß, Nuclear envelope formation, Ran, Dominant-negative mutations, Drosophila

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