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Genetics Research International
Volume 2012 (2012), Article ID 276948, 13 pages
http://dx.doi.org/10.1155/2012/276948
Review Article

Regulation of Ribosomal RNA Production by RNA Polymerase I: Does Elongation Come First?

1LBME du CNRS, 118 route de Narbonne, 31000 Toulouse, France
2Laboratoire de Biologie Moleculaire Eucaryote, Université de Toulouse, 118 route de Narbonne, 31000 Toulouse, France
3Universität Regensburg, Biochemie-Zentrum Regensburg (BZR), Lehrstuhl Biochemie III, 93053 Regensburg, Germany

Received 31 August 2011; Accepted 27 September 2011

Academic Editor: Sebastián Chávez

Copyright © 2012 Benjamin Albert et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Ribosomal RNA (rRNA) production represents the most active transcription in the cell. Synthesis of the large rRNA precursors (35–47S) can be achieved by up to 150 RNA polymerase I (Pol I) enzymes simultaneously transcribing each rRNA gene. In this paper, we present recent advances made in understanding the regulatory mechanisms that control elongation. Built-in Pol I elongation factors, such as Rpa34/Rpa49 in budding yeast and PAF53/CAST in humans, are instrumental to the extremely high rate of rRNA production per gene. rRNA elongation mechanisms are intrinsically linked to chromatin structure and to the higher-order organization of the rRNA genes (rDNA). Factors such as Hmo1 in yeast and UBF1 in humans are key players in rDNA chromatin structure in vivo. Finally, elongation factors known to regulate messengers RNA production by RNA polymerase II are also involved in rRNA production and work cooperatively with Rpa49 in vivo.