title: Dynamics and compartmentation of the nucleolar processing machinery.
abstract: In active nucleoli, machineries involved in the biogenesis of ribosomal RNAs (rRNAs) are compartmentalized. The late rRNA processing proteins are localized in the granular component (GC). Here we investigate the behavior of these proteins when production of 28S is impaired and when this blockage is reversed. The 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) provokes dispersion of rDNA clusters and we demonstrate that DRB induces disconnection of the late rRNA processing proteins from the transcription sites. These processing proteins are still associated in independent masses without detectable 28S rRNA, indicating that compartmentation of the late rRNA processing machinery is not necessarily linked to processing activity. Removing DRB reverses this disconnection and promotes rRNA processing. Nucleolar reformation occurs in two successive steps, dynamic recruitment to transcription sites of the processing proteins, followed by rDNA compaction. We demonstrate that both steps are sensitive to temperature, suggesting an energy-dependent process. Traffic of processing proteins analyzed by fluorescence recovery after photobleaching is similar in masses disconnected from transcription sites and in the granular component of the active nucleolus. This suggests that protein dynamics and interactions, and not only their processing activity, determine compartmentation of the nucleolar machineries.
authors.affiliation: Institut Jacques Monod, CNRS, University Paris VI and Paris VII, 2 place Jussieu, 75251 Paris Cedex 05, France.
authors.forename: Emilie
authors.initials: E
authors.lastname: Louvet
authors.forename: Henriette Roberte
authors.initials: HR
authors.lastname: Junéra
authors.forename: Sophie
authors.initials: S
authors.lastname: Le Panse
authors.forename: Danièle
authors.initials: D
authors.lastname: Hernandez-Verdun
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D002451:Cell Compartmentation / Q000187:drug effects / Q000502:physiology*; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D046529:Microscopy, Electron, Transmission; D017711:Nonlinear Dynamics; D009687:Nuclear Proteins / Q000187:drug effects / Q000378:metabolism*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000502:physiology; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D012339:RNA, Ribosomal, 28S / Q000187:drug effects / Q000378:metabolism; D013696:Temperature; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology*
chemical_list: D009687:Nuclear Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D012335:RNA, Ribosomal; D012339:RNA, Ribosomal, 28S; D004004:Dichlororibofuranosylbenzimidazole