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Molecular and Cellular Biology, July 2006, p. 5436-5448, Vol. 26, No. 14
0270-7306/06/$08.00+0     doi:10.1128/MCB.00230-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

RNA Polymerase I-Specific Subunit CAST/hPAF49 Has a Role in the Activation of Transcription by Upstream Binding Factor

Kostya I. Panov,1 Tatiana B. Panova,1 Olivier Gadal,2 Kaori Nishiyama,3 Takashi Saito,3 Jackie Russell,1 and Joost C. B. M. Zomerdijk1*

Division of Gene Regulation and Expression, School of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom,1 Unité de Biologie Cellulaire du Noyau, 25-28 Rue du Docteur Roux, 75724 Paris Cedex 15, France,2 Laboratory for Cell Signaling, RIKEN Research Center for Allergy and Immunology, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan3

Received 7 February 2006/ Returned for modification 10 March 2006/ Accepted 27 April 2006

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 CD3{varepsilon}-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 Iß 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.

* Corresponding author. Mailing address: Division of Gene Regulation and Expression, School of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom. Phone: 44 1382 384242. Fax: 44 1382 388072. E-mail: j.zomerdijk{at}dundee.ac.uk.

Molecular and Cellular Biology, July 2006, p. 5436-5448, Vol. 26, No. 14
0270-7306/06/$08.00+0     doi:10.1128/MCB.00230-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Beckouet, F., Labarre-Mariotte, S., Albert, B., Imazawa, Y., Werner, M., Gadal, O., Nogi, Y., Thuriaux, P. (2008). Two RNA Polymerase I Subunits Control the Binding and Release of Rrn3 during Transcription. Mol. Cell. Biol. 28: 1596-1605 [Abstract] [Full Text]  


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