Importin α Nuclear Localization Signal Binding Sites for STAT1, STAT2, and Influenza A Virus Nucleoprotein

• Published in: The Journal of biological chemistry 2003-07, Vol.278 (30), p.28193-28200
• Main Authors: Melén, Krister, Fagerlund, Riku, Franke, Jacqueline, Köhler, Matthias, Kinnunen, Leena, Julkunen, Ilkka
• Format: Article
• Language: English
• Subjects: alpha Karyopherins - metabolism; Amino Acid Sequence; Animals; Antigens, Polyomavirus Transforming - metabolism; Baculoviridae - metabolism; Binding Sites; Blotting, Western; Cell Line; Dimerization; DNA-Binding Proteins - metabolism; Electrophoresis, Polyacrylamide Gel; Humans; Insecta; Interferons - metabolism; Karyopherins - metabolism; Models, Molecular; Molecular Sequence Data; Mutagenesis, Site-Directed; Nuclear Localization Signals; Nucleocapsid Proteins; Nucleoproteins - metabolism; Phylogeny; Plasmids - metabolism; Protein Binding; Protein Isoforms; Protein Structure, Tertiary; RNA-Binding Proteins; Sequence Homology, Amino Acid; STAT1 Transcription Factor; STAT2 Transcription Factor; Trans-Activators - metabolism; Viral Core Proteins - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M303571200

Proteins actively transported into the nucleus via the classical nuclear import pathway contain nuclear localization signals (NLSs), which are recognized by the family of importin α molecules. Importin α contains 10 armadillo (arm) repeats, of which the N-terminal arm repeats 2–4 have been considered as the “major” NLS binding site. Interferon-activated, dimerized signal transducers and activators of transcription (STAT1 and STAT2) directly bind to importin α5 via a dimeric nonclassical NLS. Here we show by site-directed mutagenesis that the very C-terminal arm repeats 8 and 9 of importin α5 form a unique binding site for STAT1 homodimers and STAT1-STAT2 heterodimers. Influenza A virus nucleoprotein also contains a nonclassical NLS that is recognized by the C-terminal NLS binding site of importin α5, comprising arm repeats 7–9. Binding of influenza A virus nucleoprotein to importin α3 also occurs via the C-terminal arm repeats. Simian virus 40 large T antigen instead binds to the major N-terminal arm repeats of importin α3, indicating that one importin α molecule is able to use either its N- or C-terminal arm repeats for binding various NLS containing proteins.