title: Iwr1 directs RNA polymerase II nuclear import.
abstract: RNA polymerase (Pol) II transcribes protein-coding genes in the nucleus of eukaryotic cells and consists of 12 polypeptide subunits. It is unknown how Pol II is imported into the nucleus. Here we show that Pol II nuclear import requires the protein Iwr1 and provide evidence for cyclic Iwr1 function. Iwr1 binds Pol II in the active center cleft between the two largest subunits, maybe facilitating or sensing complete Pol II assembly in the cytoplasm. Iwr1 then uses an N-terminal bipartite nuclear localization signal that is recognized by karyopherin α to direct Pol II nuclear import. In the nucleus, Iwr1 is displaced from Pol II by transcription initiation factors and nucleic acids, enabling its export and recycling. Iwr1 function is Pol II specific, transcription independent, and apparently conserved from yeast to human.
authors.affiliation: Department of Biochemistry, Center for Integrated Protein Science Munich, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
authors.forename: Elmar
authors.initials: E
authors.lastname: Czeko
authors.forename: Martin
authors.initials: M
authors.lastname: Seizl
authors.forename: Christian
authors.initials: C
authors.lastname: Augsberger
authors.forename: Thorsten
authors.initials: T
authors.lastname: Mielke
authors.forename: Patrick
authors.initials: P
authors.lastname: Cramer
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012319:RNA Polymerase II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C544940:IWR1 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II