title: Cloning and characterization of hSRP1 gamma, a tissue-specific nuclear transport factor.
abstract: Nuclear import of proteins containing a nuclear localization signal (NLS) is dependent on the presence of a cytoplasmic NLS receptor, the GTPase Ran, and p10/ NTF2. The NLS receptor is a heterodimeric proteins consisting of subunits of approximately 60 and 97 kDa, which have been termed importin alpha/beta, karyopherin alpha/beta, or PTAC 58/ 97. Members of the 60-kDa/importin alpha subunit family directly bind to the NLS motif and have been shown to function as adaptors that tether NLS-containing proteins to the p97/ importin beta subunit and to the downstream transport machinery. Herein we report the identification and characterization of hSRP1 gamma, a human importin alpha homologue. The hSRP1 gamma protein is around 45% identical to the previously identified human importin alpha homologues hSRP1 alpha/Rch1 and NPI/ hSRP1. hSRP1 gamma can form a complex with importin beta and is able to mediate import of a BSA-NLS substrate in an in vitro nuclear import system. Interestingly, hSRP1 gamma shows a very selective expression pattern and is most abundantly expressed in skeletal muscle, representing more than 1% of the total protein in this tissue. A potential role for hSRP1 gamma in tissue-specific transport events is discussed.
authors.affiliation: Department of Microbiology and Immunology, University of California, San Francisco 94143-0414, USA.
authors.forename: M V
authors.initials: MV
authors.lastname: Nachury
authors.forename: U W
authors.initials: UW
authors.lastname: Ryder
authors.forename: A I
authors.initials: AI
authors.lastname: Lamond
authors.forename: K
authors.initials: K
authors.lastname: Weis
mesh_terms: D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D009928:Organ Specificity; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D028901:alpha Karyopherins
chemical_list: D002352:Carrier Proteins; D009687:Nuclear Proteins; D028901:alpha Karyopherins