title: A distinct and parallel pathway for the nuclear import of an mRNA-binding protein.
abstract: Three independent pathways of nuclear import have so far been identified in yeast, each mediated by cognate nuclear transport factors, or karyopherins. Here we have characterized a new pathway to the nucleus, mediated by Mtr10p, a protein first identified in a screen for strains defective in polyadenylated RNA export. Mtr10p is shown to be responsible for the nuclear import of the shuttling mRNA-binding protein Npl3p. A complex of Mtr10p and Npl3p was detected in cytosol, and deletion of Mtr10p was shown to lead to the mislocalization of nuclear Npl3p to the cytoplasm, correlating with a block in import. Mtr10p bound peptide repeat-containing nucleoporins and Ran, suggesting that this import pathway involves a docking step at the nuclear pore complex and is Ran dependent. This pathway of Npl3p import is distinct and does not appear to overlap with another known import pathway for an mRNA-binding protein. Thus, at least two parallel pathways function in the import of mRNA-binding proteins, suggesting the need for the coordination of these pathways.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York 10021, USA.
authors.forename: L F
authors.initials: LF
authors.lastname: Pemberton
authors.forename: J S
authors.initials: JS
authors.lastname: Rosenblum
authors.forename: G
authors.initials: G
authors.lastname: Blobel
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins; D010455:Peptides / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D028961:beta Karyopherins
chemical_list: D005656:Fungal Proteins; C080324:GSP1 protein, S cerevisiae; C110033:MTR10 protein, S cerevisiae; C077734:NPL3 protein, S cerevisiae; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D010455:Peptides; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D028961:beta Karyopherins; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins