title: The conserved amino-terminal domain of hSRP1 alpha is essential for nuclear protein import.
abstract: Nuclear proteins are targeted through the nuclear pore complex (NPC) in an energy-dependent reaction. The import reaction is mediated by nuclear localization sequences (NLS) in the substrate which are recognized by heterodimeric cytoplasmic receptors. hSRP1 alpha is an NLS-binding subunit of the human NLS receptor complex and is complexed in vivo with a second subunit of 97 kDa (p97). We show here that a short amino-terminal domain in hSRP1 alpha is necessary and sufficient for its interaction with p97. This domain is conserved in other SRP1-like proteins and its fusion to a cytoplasmic reporter protein is sufficient to promote complete nuclear import, circumventing the usual requirement for an NLS receptor interaction. The same amino-terminal domain inhibits import of NLS-containing proteins when added to an in vitro nuclear transport assay. While full-length hSRP alpha is able to leave the nucleus, the amino-terminal domain alone is not sufficient to promote exit. We conclude that hSRP1 alpha functions as an adaptor to tether NLS-containing substrates to the protein import machinery.
authors.affiliation: European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Weis
authors.forename: U
authors.initials: U
authors.lastname: Ryder
authors.forename: A I
authors.initials: AI
authors.lastname: Lamond
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D001693:Biological Transport, Active; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; C075564:NOLC1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; C094680:nuclear protein import factor p97