|
|
|
|
|
||
|
|||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | |||||
Research Article |
1 Unité MéDIAN, CNRS UMR 6142, UFR de Pharmacie, 51 rue
Cognacq-Jay, 51096 Reims Cedex, France
2 DTI, UMR 6107, UFR de Sciences, BP 1039, 51687 Reims Cedex, France
3 Laboratoire de Biologie Cellulaire et Tissulaire, Université de
Liège, 20 rue de Pitteurs, 4020 Liège, Belgium
4 IFR53, 51 rue Cognacq-Jay, 51096 Reims Cedex, France
* Author for correspondence (e-mail: dominique.ploton{at}univ-reims.fr )
Accepted 23 May 2002
In this work, we have localized transcribing rRNA genes at the ultrastructural level and described their three-dimensional organization within the nucleolus by electron tomography. Isolated nucleoli, which exhibit a reduced transcriptional rate, were used to determine the sites of initial BrUTP incorporation (i.e. rRNA synthesis by the transcriptional machinery). Using pulse-chase experiments with BrUTP and an elongation inhibitor, cordycepin, it was possible to precisely localize the initial sites of BrUTP incorporation. Our data show that BrUTP incorporation initially takes place in the fibrillar centers and that elongating rRNAs rapidly enter the surrounding dense fibrillar component. Furthermore, we investigated the spatial arrangement of RNA polymerase I molecules within the whole volume of the fibrillar centers. Electron tomography was performed on thick sections of cells that had been labeled with anti-RNA polymerase I antibodies prior to embedding. Detailed tomographic analyses revealed that RNA polymerase I molecules are mainly localized within discrete clusters. In each of them, RNA polymerase I molecules were grouped as several coils, 60 nm in diameter. Overall, these findings have allowed us to propose a model for the three-dimensional organization of transcribing rDNA genes within the nucleolus.
Key words: Cell nucleolus, RNA polymerase I, Pre-ribosomal RNA, BrUTP incorporation, Electron tomography
Related articles in JCS:
This article has been cited by other articles:
|
|
 |
|
  J. J. Petricka and T. M. Nelson Arabidopsis Nucleolin Affects Plant Development and Patterning Plant Physiology, May 1, 2007; 144(1): 173 - 186. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Derenzini, G. Pasquinelli, M.-F. O'Donohue, D. Ploton, and M. Thiry Structural and Functional Organization of Ribosomal Genes within the Mammalian Cell Nucleolus J. Histochem. Cytochem., February 1, 2006; 54(2): 131 - 145. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. W. Lam, L. Trinkle-Mulcahy, and A. I. Lamond The nucleolus J. Cell Sci., April 1, 2005; 118(7): 1335 - 1337. [Full Text] [PDF]
|
|
|
|
 |
|
 M. O. Christensen, R. M. Krokowski, H. U. Barthelmes, R. Hock, F. Boege, and C. Mielke Distinct Effects of Topoisomerase I and RNA Polymerase I Inhibitors Suggest a Dual Mechanism of Nucleolar/Nucleoplasmic Partitioning of Topoisomerase I J. Biol. Chem., May 21, 2004; 279(21): 21873 - 21882. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Halkidou, I. R. Logan, S. Cook, D. E. Neal, and C. N. Robson Putative involvement of the histone acetyltransferase Tip60 in ribosomal gene transcription Nucleic Acids Res., March 11, 2004; 32(5): 1654 - 1665. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Cheutin, M.-F. O'Donohue, A. Beorchia, C. Klein, H. Kaplan, and D. Ploton Three-dimensional Organization of pKi-67: A Comparative Fluorescence and Electron Tomography Study Using Fluoronanogold J. Histochem. Cytochem., November 1, 2003; 51(11): 1411 - 1423. [Abstract] [Full Text] [PDF]
|
|
