title: Rrn3 phosphorylation is a regulatory checkpoint for ribosome biogenesis.
abstract: Cycloheximide inhibits ribosomal DNA (rDNA) transcription in vivo. The mouse homologue of yeast Rrn3, a polymerase-associated transcription initiation factor, can complement extracts from cycloheximide-treated mammalian cells. Cycloheximide inhibits the phosphorylation of Rrn3 and causes its dissociation from RNA polymerase I. Rrn3 interacts with the rpa43 subunit of RNA polymerase I, and treatment with cycloheximide inhibits the formation of a Rrn3.rpa43 complex in vivo. Rrn3 produced in Sf9 cells but not in bacteria interacts with rpa43 in vitro, and such interaction is dependent upon the phosphorylation state of Rrn3. Significantly, neither dephosphorylated Rrn3 nor Rrn3 produced in Escherichia coli can restore transcription by extracts from cycloheximide-treated cells. These results suggest that the phosphorylation state of Rrn3 regulates rDNA transcription by determining the steady-state concentration of the Rrn3.RNA polymerase I complex within the nucleolus.
authors.affiliation: Sigfried and Janet Weis Center for Research, Geisinger Clinic, 100 N. Academy Avenue, Danville, PA 17821, USA.
authors.forename: Alice H
authors.initials: AH
authors.lastname: Cavanaugh
authors.forename: Iwona
authors.initials: I
authors.lastname: Hirschler-Laszkiewicz
authors.forename: Qiyue
authors.initials: Q
authors.lastname: Hu
authors.forename: Miroslav
authors.initials: M
authors.lastname: Dundr
authors.forename: Tom
authors.initials: T
authors.lastname: Smink
authors.forename: Tom
authors.initials: T
authors.lastname: Misteli
authors.forename: Lawrence I
authors.initials: LI
authors.lastname: Rothblum
mesh_terms: D016475:3T3 Cells; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002466:Cell Nucleolus; D002467:Cell Nucleus / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D005816:Genetic Complementation Test; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D007313:Insecta; D051379:Mice; D008954:Models, Biological; D010449:Peptide Mapping; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D035463:Pol1 Transcription Initiation Complex Proteins; D011233:Precipitin Tests; D011485:Protein Binding; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D035463:Pol1 Transcription Initiation Complex Proteins; D011500:Protein Synthesis Inhibitors; D011994:Recombinant Proteins; C491074:Rrn3 protein, mouse; D014157:Transcription Factors; D003513:Cycloheximide; D010744:Phosphoric Monoester Hydrolases