Small nucleolar ribonucleoprotein particles (snoRNPs) mainly catalyze the modification of rRNA. The two major classes of snoRNPs, box H/ACA and box C/D, function in the pseudouridylation and 2'-O-methylation, respectively, of specific nucleotides. The emerging view based on studies in yeast is that each class of snoRNPs is composed of a unique set of proteins. Here we present a characterization of mammalian snoRNPs. We show that the previously characterized NAP57 is specific for box H/ACA snoRNPs, whereas the newly identified NAP65, the rat homologue of yeast Nop5/58p, is a component of the box C/D class. Using coimmunoprecipitation experiments, we show that the nucleolar and coiled-body protein Nopp140 interacts with both classes of snoRNPs. This interaction is corroborated in vivo by the exclusive depletion of snoRNP proteins from nucleoli in cells transfected with a dominant negative Nopp140 construct. Interestingly, RNA polymerase I transcription is arrested in nucleoli depleted of snoRNPs, raising the possibility of a feedback mechanism between rRNA modification and transcription. Moreover, the Nopp140-snoRNP interaction appears to be conserved in yeast, because depletion of Srp40p, the yeast Nopp140 homologue, in a conditional lethal strain induces the loss of box H/ACA small nucleolar RNAs. We propose that Nopp140 functions as a chaperone of snoRNPs in yeast and vertebrate cells.
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Evidence ID | Analyze ID | Gene/Complex | Systematic Name/Complex Accession | Qualifier | Gene Ontology Term ID | Gene Ontology Term | Aspect | Annotation Extension | Evidence | Method | Source | Assigned On | Reference |
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Evidence ID | Analyze ID | Gene | Gene Systematic Name | Phenotype | Experiment Type | Experiment Type Category | Mutant Information | Strain Background | Chemical | Details | Reference |
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Evidence ID | Analyze ID | Gene | Gene Systematic Name | Disease Ontology Term | Disease Ontology Term ID | Qualifier | Evidence | Method | Source | Assigned On | Reference |
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Evidence ID | Analyze ID | Regulator | Regulator Systematic Name | Target | Target Systematic Name | Direction | Regulation of | Happens During | Regulator Type | Direction | Regulation Of | Happens During | Method | Evidence | Strain Background | Reference |
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Site | Modification | Modifier | Source | Reference |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Assay | Annotation | Action | Modification | Source | Reference | Note |
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Complement ID | Locus ID | Gene | Species | Gene ID | Strain background | Direction | Details | Source | Reference |
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Evidence ID | Analyze ID | Dataset | Description | Keywords | Number of Conditions | Reference |
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