Conserved composition of mammalian box H/ACA and box C/D small nucleolar ribonucleoprotein particles and their interaction with the common factor Nopp140.
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.
Yang
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Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Isaac
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Wang
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Dragon
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Pogacic
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Meier
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D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002466:Cell Nucleolus / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics; D004843:Epistasis, Genetic; D005816:Genetic Complementation Test; D006836:Hydro-Lyases; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D012318:RNA Polymerase I / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D051381:Rats; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear; D020718:Ribonucleoproteins, Small Nucleolar / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D000068103:Serine-Arginine Splicing Factors; D014158:Transcription, Genetic / Q000235:genetics / Q000502:physiology
D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; C107170:NAP57; C075564:NOLC1 protein, human; C438199:NOP58 protein, S cerevisiae; C513067:Nolc1 protein, rat; C499060:Nop58 protein, rat; D009687:Nuclear Proteins; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D020718:Ribonucleoproteins, Small Nucleolar; D029701:Saccharomyces cerevisiae Proteins; D000068103:Serine-Arginine Splicing Factors; D012318:RNA Polymerase I; D006836:Hydro-Lyases; C082278:CBF5 protein, S cerevisiae