The NPI-1/NPI-3 (karyopherin alpha) binding site on the influenza a virus nucleoprotein NP is a nonconventional nuclear localization signal.
Two cellular proteins, NPI-1 and NPI-3, were previously identified through their interaction with the influenza virus nucleoprotein (NP) by using the yeast two-hybrid system. These proteins were then shown to act as general transport factors (karyopherin alpha) and nuclear pore-docking proteins to facilitate the transport of the NP and of viral RNA into the nucleus. The yeast two-hybrid assay has now been used to identify the specific domains on the NP that bind to the NPI proteins. Mutational analysis including alanine scanning identified the motifs SxGTKRSYxxM and TKRSxxxM, which are required for binding to NPI-1 and NPI-3, respectively. These sequences were shown to possess nuclear localization signal (NLS) activity following expression of fusion proteins in HeLa cells. These sequences represent a novel nonconventional NLS motif. Another NLS activity not mediated by the NPI binding sites is associated with noncontiguous sequences in the NP.
Wang
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Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Palese
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O'Neill
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D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009980:Influenza A virus / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins / Q000737:chemistry* / Q000378:metabolism; D010449:Peptide Mapping; D021382:Protein Sorting Signals / Q000737:chemistry*; D016601:RNA-Binding Proteins; D015398:Signal Transduction / Q000502:physiology; D014758:Viral Core Proteins / Q000737:chemistry* / Q000378:metabolism; D028901:alpha Karyopherins
D002352:Carrier Proteins; C048842:NP protein, Influenza A virus; D009687:Nuclear Proteins; D019590:Nucleocapsid Proteins; D009698:Nucleoproteins; D021382:Protein Sorting Signals; D016601:RNA-Binding Proteins; D014758:Viral Core Proteins; D028901:alpha Karyopherins; C087978:karyopherin alpha 2