title: Nuclear import of zinc binuclear cluster proteins proceeds through multiple, overlapping transport pathways.
abstract: In Aspergillus nidulans, the high transcriptional level of the ethanol utilization pathway genes (alc) is regulated by the specific activator AlcR. Here we have analyzed the mechanism of the nuclear import of AlcR, as well as that of other proteins belonging to the Zn(2)Cys(6) binuclear cluster family. The nuclear localization signal of AlcR maps within the N-terminal 75 amino acid residues and overlaps with its DNA-binding domain. It consists of five clusters rich in basic residues. Four of them are necessary and sufficient for nuclear targeting. The first two basic regions are crucial for both nuclear localization and recognition of AlcR-specific DNA targets. This nuclear localization signal (NLS) motif is recognized by the nuclear transport machinery of Saccharomyces cerevisiae and requires both Ran/Gsp1p activity and specific transport receptors. AlcR can be imported into nuclei via multiple transport pathways mediated by a distinct set of karyopherins composed of Kap104p, Sxm1p, and Nmd5p transport receptors. The two former karyopherins interact with the NLS of AlcR directly. Other Zn binuclear cluster proteins from S. cerevisiae, such as Gal4p and Pdr3p, also appear to be transported to the nuclei in a nonclassical, importin-alpha-independent manner and can share common importin beta receptors.
authors.affiliation: Institut de Génétique et Microbiologie, Université Paris-Sud, UMR 8621 CNRS, Centre d'Orsay, 91405 Orsay Cedex, France. felenbok@igmors.u-psud.fr
authors.forename: Igor
authors.initials: I
authors.lastname: Nikolaev
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Cochet
authors.forename: Béatrice
authors.initials: B
authors.lastname: Felenbok
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D001665:Binding Sites / Q000502:physiology; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015032:Zinc / Q000378:metabolism; D028901:alpha Karyopherins / Q000378:metabolism
chemical_list: C074202:ALCR protein, Aspergillus nidulans; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; C080324:GSP1 protein, S cerevisiae; D028884:Karyopherins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D028901:alpha Karyopherins; D020559:Monomeric GTP-Binding Proteins; D015032:Zinc