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Mol. Cell. Biol. doi:10.1128/MCB.01464-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Two RNA Polymerase I Subunits Control the Binding and Release of Rrn3 during Transcription

CEA, IbiTec-S, Service de Biologie Intégrative & Génétique Moléculaire. Gif sur Yvette, cedex. F-91191. FRANCE.; Saitama Medical University, Department of Molecular Biology. 38 Morohongo, Moroyama. Iruma-Gun, Saitama 350-04. JAPAN.; Organisation et Dynamique Nucléaire, LBME-CNRS, Université de Toulouse, 118 route de Narbonne. Toulouse, F-31000. FRANCE

^* To whom correspondence should be addressed. Email: pierre.thuriaux{at}cea.fr.

	Abstract

Rpa34 and Rpa49 are non-essential subunits of RNA polymerase I, conserved from yeast to man. Rpa34 binds an N-terminal region of Rpa49 in a two-hybrid assay and is lost from RNA polymerase in an rpa49 mutant lacking this Rpa34-binding domain, whereas rpa34 weakens the binding of Rpa49 to RNA polymerase. rpa34 is caffeine-sensitive and is lethal in top1 and in rpa14, rpa135-L656P and rpa135-D398N RNA polymerase mutants. These defects are shared with rpa49 and suppressed by over-expressing Rpa49, and are thus presumably mediated by Rpa49 itself. rpa49 mutants lacking the Rpa34-binding domain essentially behave like rpa34, but rpa49 and rpa49-338::HIS3 (lacking the conserved C-end of Rpa49) reduce polymerase occupancy at 30°C, fail to grow at 25°C and are sensitive to 6-azauracil and mycophenolate. Mycophenolate almost fully dissociates the mutant polymerase from its rDNA template. These mutants have a dual effect on the Rrn3/TIF-IA factor. They partly impair its recruitment to the rDNA promoter, which is bypassed by rpa43-35,326, an N-terminal deletion of the Rpa43 subunit, and strongly reduce the release of the Rrn3 initiation factor during elongation. These data suggest a dual role of the Rpa49-Rpa34 dimer during the recruitment of Rrn3 and its subsequent dissociation from the elongating polymerase.

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