Melen Krister, Fagerlund Riku, Franke Jacqueline, Kohler Matthias, Kinnunen Leena, Julkunen Ilkka
Laboratory of Infectious Disease Immunology, Department of Microbiology, National Public Health Institute, FIN-00300 Helsinki, Finland.
J Biol Chem. 2003 Jul 25;278(30):28193-200. doi: 10.1074/jbc.M303571200. Epub 2003 May 9.
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.
通过经典核输入途径被主动转运到细胞核中的蛋白质含有核定位信号（NLSs），这些信号被输入蛋白α分子家族所识别。输入蛋白α含有10个犰狳（arm）重复序列，其中N端的第2 - 4个arm重复序列被认为是“主要”的NLS结合位点。干扰素激活的、二聚化的信号转导子和转录激活子（STAT1和STAT2）通过二聚体非经典NLS直接与输入蛋白α5结合。在这里，我们通过定点诱变表明，输入蛋白α5的最C端的arm重复序列8和9形成了STAT1同二聚体和STAT1 - STAT2异二聚体的独特结合位点。甲型流感病毒核蛋白也含有一个非经典NLS，该NLS被输入蛋白α5的C端NLS结合位点所识别，该位点由arm重复序列7 - 9组成。甲型流感病毒核蛋白与输入蛋白α3的结合也通过C端的arm重复序列发生。而猴病毒40大T抗原则与输入蛋白α3的主要N端arm重复序列结合，这表明一个输入蛋白α分子能够利用其N端或C端的arm重复序列来结合各种含有NLS的蛋白质。
