title: Cytosolic proteins that specifically bind nuclear location signals are receptors for nuclear import.
abstract: We have purified two major polypeptides of 54 and 56 kd from bovine erythrocytes that specifically bind the nuclear location sequence (NLS) of the SV40 large T antigen. When added to a permeabilized cell system for nuclear import, the purified proteins increase by 2- to 3-fold the nuclear accumulation of a fluorescent protein containing the large T antigen NLS. The import stimulation is saturable and dependent upon the presence of cytosol. Nuclear protein accumulation in vitro is sensitive to inactivation by N-ethylmaleimide (NEM). NEM inactivation can be overcome by addition of the purified NLS-binding proteins to the import system. NEM treatment of the purified proteins abolishes their ability to stimulate import but does not affect NLS binding. Our results indicate that the NLS-binding proteins are NEM-sensitive receptors for nuclear import. At least one other NEM-sensitive cytosolic activity and an NEM-insensitive cytosolic activity are also necessary for protein import in vitro.
authors.affiliation: Department of Cell, Molecular and Structural Biology, Northwestern University Medical School, Chicago, Illinois 60611.
authors.forename: S A
authors.initials: SA
authors.lastname: Adam
authors.forename: L
authors.initials: L
authors.lastname: Gerace
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport; D002417:Cattle; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012995:Solubility
chemical_list: D000952:Antigens, Polyomavirus Transforming; D009687:Nuclear Proteins; D010455:Peptides; D011956:Receptors, Cell Surface; D005033:Ethylmaleimide