Importin alpha nuclear localization signal binding sites for STAT1, STAT2, and influenza A virus nucleoprotein.
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 alpha molecules. Importin alpha 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 alpha5 via a dimeric nonclassical NLS. Here we show by site-directed mutagenesis that the very C-terminal arm repeats 8 and 9 of importin alpha5 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 alpha5, comprising arm repeats 7-9. Binding of influenza A virus nucleoprotein to importin alpha3 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 alpha3, indicating that one importin alpha molecule is able to use either its N- or C-terminal arm repeats for binding various NLS containing proteins.
Laboratory of Infectious Disease Immunology, Department of Microbiology, National Public Health Institute, FIN-00300 Helsinki, Finland. krister.melen@ktl.fi
Krister
K
Melen
Riku
R
Fagerlund
Jacqueline
J
Franke
Matthias
M
Kohler
Leena
L
Kinnunen
Ilkka
I
Julkunen
D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism; D016367:Baculoviridae / Q000378:metabolism; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007313:Insecta; D007372:Interferons / Q000378:metabolism; D028884:Karyopherins / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019913:Nuclear Localization Signals; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins / Q000378:metabolism*; D010802:Phylogeny; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000378:metabolism*; D014758:Viral Core Proteins / Q000378:metabolism*; D028901:alpha Karyopherins / Q000378:metabolism*
D000952:Antigens, Polyomavirus Transforming; D004268:DNA-Binding Proteins; C423142:KPNA1 protein, human; D028884:Karyopherins; C048842:NP protein, Influenza A virus; D019913:Nuclear Localization Signals; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D015534:Trans-Activators; D014758:Viral Core Proteins; D028901:alpha Karyopherins; D007372:Interferons