title: RNA polymerase I-specific subunit CAST/hPAF49 has a role in the activation of transcription by upstream binding factor.
abstract: Eukaryotic RNA polymerases are large complexes, 12 subunits of which are structurally or functionally homologous across the three polymerase classes. Each class has a set of specific subunits, likely targets of their cognate transcription factors. We have identified and characterized a human RNA polymerase I (Pol I)-specific subunit, previously identified as ASE-1 (antisense of ERCC1) and as CD3epsilon-associated signal transducer (CAST), and here termed CAST or human Pol I-associated factor of 49 kDa (hPAF49), after mouse orthologue PAF49. We provide evidence for growth-regulated Tyr phosphorylation of CAST/hPAF49, specifically in initiation-competent Pol Ibeta complexes in HeLa cells, at a conserved residue also known to be important for signaling during T-cell activation. CAST/hPAF49 can interact with activator upstream binding factor (UBF) and, weakly, with selectivity factor 1 (SL1) at the rDNA (ribosomal DNA repeat sequence encoding the 18S, 5.8S, and 28S rRNA genes) promoter. CAST/hPAF49-specific antibodies and excess CAST/hPAF49 protein, which have no effect on basal Pol I transcription, inhibit UBF-activated transcription following functional SL1-Pol I-rDNA complex assembly and disrupt the interaction of UBF with CAST/hPAF49, suggesting that interaction of this Pol I-specific subunit with UBF is crucial for activation. Drawing on parallels between mammalian and Saccharomyces cerevisiae Pol I transcription machineries, we advance one model for CAST/hPAF49 function in which the network of interactions of Pol I-specific subunits with UBF facilitates conformational changes of the polymerase, leading to stabilization of the Pol I-template complex and, thereby, activation of transcription.
authors.affiliation: Division of Gene Regulation and Expression, School of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom.
authors.forename: Kostya I
authors.initials: KI
authors.lastname: Panov
authors.forename: Tatiana B
authors.initials: TB
authors.lastname: Panova
authors.forename: Olivier
authors.initials: O
authors.lastname: Gadal
authors.forename: Kaori
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Saito
authors.forename: Jackie
authors.initials: J
authors.lastname: Russell
authors.forename: Joost C B M
authors.initials: JC
authors.lastname: Zomerdijk
mesh_terms: D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D010766:Phosphorylation; D035463:Pol1 Transcription Initiation Complex Proteins / Q000378:metabolism*; D021122:Protein Subunits; D012318:RNA Polymerase I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014443:Tyrosine / Q000737:chemistry
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D021122:Protein Subunits; C063844:transcription factor UBF; D014443:Tyrosine; C119975:POLR1G protein, human; D012318:RNA Polymerase I