Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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COS Cells
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Cell Nucleolus / chemistry
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Cell Nucleolus / enzymology
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Cell Nucleolus / metabolism
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Conserved Sequence* / genetics
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Epistasis, Genetic
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Genetic Complementation Test
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Hydro-Lyases*
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Microtubule-Associated Proteins / genetics
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Microtubule-Associated Proteins / metabolism
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Molecular Chaperones / genetics
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Molecular Chaperones / metabolism
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Molecular Sequence Data
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Molecular Weight
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Mutation / genetics
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Nuclear Proteins / chemistry
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Nuclear Proteins / deficiency
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism*
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Phosphoproteins / deficiency
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Phosphoproteins / genetics
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Phosphoproteins / metabolism*
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Protein Binding
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RNA Polymerase I / metabolism
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RNA-Binding Proteins / genetics
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RNA-Binding Proteins / metabolism
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Rats
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Ribonucleoproteins / chemistry
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Ribonucleoproteins / metabolism
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Ribonucleoproteins, Small Nuclear*
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Ribonucleoproteins, Small Nucleolar / chemistry*
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Ribonucleoproteins, Small Nucleolar / deficiency
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Ribonucleoproteins, Small Nucleolar / genetics
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Ribonucleoproteins, Small Nucleolar / metabolism*
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Saccharomyces cerevisiae / genetics
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Saccharomyces cerevisiae Proteins*
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Serine-Arginine Splicing Factors
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Transcription, Genetic / genetics
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Transcription, Genetic / physiology
Substances
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Microtubule-Associated Proteins
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Molecular Chaperones
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NAP57
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NOLC1 protein, human
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NOP58 protein, S cerevisiae
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Nolc1 protein, rat
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Nop58 protein, rat
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Nuclear Proteins
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Phosphoproteins
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RNA-Binding Proteins
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Ribonucleoproteins
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Ribonucleoproteins, Small Nuclear
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Ribonucleoproteins, Small Nucleolar
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Saccharomyces cerevisiae Proteins
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Serine-Arginine Splicing Factors
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RNA Polymerase I
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Hydro-Lyases
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CBF5 protein, S cerevisiae