title: Nuclear localization signal recognition causes release of importin-alpha from aggregates in the cytosol.
abstract: Importin-alpha is a cytosolic receptor that recognizes classical Nuclear Localization Signals (NLSs) and mediates import into the nucleus. We have used a number of methods to investigate the aggregation state of Xenopus importin-alpha both as a recombinant, purified protein and in cytosolic extracts. We have found that recombinant importin-alpha aggregates at a protein concentration similar to that estimated to be present in the Xenopus cytoplasm, and that the importin-alpha aggregation is relieved by NLS peptide binding, with the importin-alpha then binding the NLS as a monomer. We have also found that in HeLa cytosolic extracts, importin-alpha is present in an aggregated form. Similarly to the purified importin-alpha aggregation, NLS peptides relieve the aggregation of importin-alpha in the cytosol. These observations indicate that aggregation of importin-alpha in the cytosol may be an intrinsic property of the import receptor and may be functionally related to NLS binding.Our results suggest a novel mechanism for NLS recognition, whereby NLSs mediate disassembly of importin-alpha aggregates in the cytosol.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, UK.
authors.forename: P
authors.initials: P
authors.lastname: Percipalle
authors.forename: P J
authors.initials: PJ
authors.lastname: Butler
authors.forename: J T
authors.initials: JT
authors.lastname: Finch
authors.forename: D A
authors.initials: DA
authors.lastname: Jans
authors.forename: D
authors.initials: D
authors.lastname: Rhodes
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003600:Cytosol / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D009685:Nuclear Envelope / Q000378:metabolism; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D014461:Ultracentrifugation; D014981:Xenopus
chemical_list: D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D011994:Recombinant Proteins