title: Biogenesis of RNA polymerases II and III requires the conserved GPN small GTPases in Saccharomyces cerevisiae.
abstract: The GPN proteins are a poorly characterized and deeply evolutionarily conserved family of three paralogous small GTPases, Gpn1, 2, and 3. The founding member, GPN1/NPA3/XAB1, is proposed to function in nuclear import of RNA polymerase II along with a recently described protein called Iwr1. Here we show that the previously uncharacterized protein Gpn2 binds both Gpn3 and Npa3/Gpn1 and that temperature-sensitive alleles of Saccharomyces cerevisiae GPN2 and GPN3 exhibit genetic interactions with RNA polymerase II mutants, hypersensitivity to transcription inhibition, and defects in RNA polymerase II nuclear localization. Importantly, we identify previously unrecognized RNA polymerase III localization defects in GPN2, GPN3, and IWR1 mutant backgrounds but find no localization defects of unrelated nuclear proteins or of RNA polymerase I. Previously, it was unclear whether the GPN proteins and Iwr1 had overlapping function in RNA polymerase II assembly or import. In this study, we show that the nuclear import defect of iwr1Δ, but not the GPN2 or GPN3 mutant defects, is partially suppressed by fusion of a nuclear localization signal to the RNA polymerase II subunit Rpb3. These data, combined with strong genetic interactions between GPN2 and IWR1, suggest that the GPN proteins function upstream of Iwr1 in RNA polymerase II and III biogenesis. We propose that the three GPN proteins execute a common, and likely essential, function in RNA polymerase assembly and transport.
authors.affiliation: Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Sean W
authors.initials: SW
authors.lastname: Minaker
authors.forename: Megan C
authors.initials: MC
authors.lastname: Filiatrault
authors.forename: Shay
authors.initials: S
authors.lastname: Ben-Aroya
authors.forename: Philip
authors.initials: P
authors.lastname: Hieter
authors.forename: Peter C
authors.initials: PC
authors.lastname: Stirling
mesh_terms: D021581:Active Transport, Cell Nucleus; D000483:Alleles; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000201:enzymology* / Q000378:metabolism; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D019913:Nuclear Localization Signals; D011485:Protein Binding; D055503:Protein Multimerization; D021381:Protein Transport; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D012320:RNA Polymerase III / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; C544940:IWR1 protein, S cerevisiae; D019913:Nuclear Localization Signals; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II; C112110:RPB3 protein, S cerevisiae; D012320:RNA Polymerase III; C582594:GPN2 protein, S cerevisiae; C582595:GPN3 protein, S cerevisiae; C568359:Npa3 protein, S cerevisiae; D020559:Monomeric GTP-Binding Proteins