title: Iwr1 protein is important for preinitiation complex formation by all three nuclear RNA polymerases in Saccharomyces cerevisiae.
abstract: BACKGROUND
  Iwr1, a protein conserved throughout eukaryotes, was originally identified by its physical interaction with RNA polymerase (Pol) II.
  
  
  RESULTS
  Here, we identify Iwr1 in a genetic screen designed to uncover proteins involved in Pol III transcription in S. cerevisiae. Iwr1 is important for Pol III transcription, because an iwr1 mutant strain shows reduced association of TBP and Pol III at Pol III promoters, a decreased rate of Pol III transcription, and lower steady-state levels of Pol III transcripts. Interestingly, an iwr1 mutant strain also displays reduced association of TBP to Pol I-transcribed genes and of both TBP and Pol II to Pol II-transcribed promoters. Despite this, rRNA and mRNA levels are virtually unaffected, suggesting a post-transcriptional mechanism compensating for the occupancy defect.
  
  
  CONCLUSIONS
  Thus, Iwr1 plays an important role in preinitiation complex formation by all three nuclear RNA polymerases.
authors.affiliation: Department of Molecular Biology, Umeå University, Umeå, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Esberg
authors.forename: Zarmik
authors.initials: Z
authors.lastname: Moqtaderi
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Fan
authors.forename: Jian
authors.initials: J
authors.lastname: Lu
authors.forename: Kevin
authors.initials: K
authors.lastname: Struhl
authors.forename: Anders
authors.initials: A
authors.lastname: Byström
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology*; D004275:DNA, Ribosomal / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics* / Q000378:metabolism; D056426:Genetic Loci / Q000235:genetics; D007700:Kinetics; D009154:Mutation; D010430:Pentosyltransferases / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D035181:TATA-Box Binding Protein / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D002352:Carrier Proteins; D004275:DNA, Ribosomal; C544940:IWR1 protein, S cerevisiae; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D035181:TATA-Box Binding Protein; D012343:RNA, Transfer; D010430:Pentosyltransferases; C090456:RIT1 protein, S cerevisiae; D012321:DNA-Directed RNA Polymerases