Topic
Nucleolus
About: Nucleolus is a research topic. Over the lifetime, 5873 publications have been published within this topic receiving 232435 citations. The topic is also known as: GO:0005730 & cell nucleolus.
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TL;DR: It is concluded that Krr1p physically and functionally interacts with Kri1p to form a complex which is required for 40S ribosome biogenesis in the nucleolus of Saccharomyces cerevisiae.
Abstract: Using a two-hybrid screening with TOM1, a putative ubiquitin-ligase gene of Saccharomyces cerevisiae ,w e isolated KRR1, a homologue of human HRB2 (for human immunodeficiency virus type 1 Rev-binding protein 2). To characterize the gene function, we constructed temperature-sensitive krr1 mutants and isolated two multicopy suppressors. One suppressor is RPS14A, encoding a 40S ribosomal protein. The C-terminaltruncated rpS14p, which was reported to have diminished binding activity to 18S rRNA, failed to suppress the krr1 mutant. The other suppressor is a novel gene, KRI1 (for KRR1 interacting protein; YNL308c). KRI1 is essential for viability, and Kri1p is localized to the nucleolus. We constructed a galactose-dependent kri1 strain by placing KRI1 under control of the GAL1 promoter, so that expression of KRI1 was shut off when transferring the culture to glucose medium. Polysome and 40S ribosome fractions were severely decreased in the krr1 mutant and Kri1p-depleted cells. Pulse-chase analysis of newly synthesized rRNAs demonstrated that 18S rRNA is not produced in either mutant. However, wild-type levels of 25S rRNA are made in either mutant. Northern analysis revealed that the steady-state levels of 18S rRNA and 20S pre-rRNAs were reduced in both mutants. Precursors for 18S rRNA were detected but probably very unstable in both mutants. A myc-tagged Kri1p coimmunoprecipitated with a hemagglutinin-tagged Krr1p. Furthermore, the krr1 mutant protein was defective in its interaction with Kri1p. These data lead us to conclude that Krr1p physically and functionally interacts with Kri1p to form a complex which is required for 40S ribosome biogenesis in the nucleolus.
72 citations
TL;DR: This work identifies a unique amino acid substitution in the P loop motif (K454A) that uncouples nucleolar localization and E3 ubiquitin ligase activity of Mdm2 and leads to upregulation of the E3 activity both in human cells and in Caenorhabditis elegans.
72 citations
TL;DR: The results add support to a recently proposed model in which the nucleolus serves as a p53-uspstream sensor of stress, and where ARF links nucleolar stress signals to nucleoplasmic effectors of the stress response.
Abstract: The p53/p14ARF/mdm2 stress response pathway plays a central role in mediating cellular responses to oncogene activation, genome instability, and therapy-induced DNA damage. Abrogation of the pathway occurs in most if not all cancers, and may be essential for tumor development. The high frequency with which the pathway is disabled in cancer and the fact that the pathway appears to be incompatible with tumor cell growth, has made it an important point of focus in cancer research and therapeutics development. Recently, Nucleophosmin (NPM, B23, NO38 and numatrin), a multifunctional nucleolar protein, has emerged as a p14ARF binding protein and regulator of p53. While complex formation between ARF and NPM retains ARF in the nucleolus and prevents ARF from activating p53, DNA damaging treatments promote a transient subnuclear redistribution of ARF to the nucleoplasm, where it interacts with mdm2 and promotes p53 activation. The results add support to a recently proposed model in which the nucleolus serves as a p53-uspstream sensor of stress, and where ARF links nucleolar stress signals to nucleoplasmic effectors of the stress response. A better understanding of ARF’s nucleolar interactions could further elucidate the regulation of the p53 pathway and suggest new therapeutic approaches to restore p53 function.
72 citations
TL;DR: immunoprecipitation from nuclear extracts demonstrates that hNop5/Nop58 interacts with the box C/D family of snoRNAs, and joins fibrillarin as the second such component identified and characterized in metazoans.
Abstract: We have identified an apparent human homolog of the yeast Nop5/Nop58 protein hNop5/Nop58 codes for a protein of predicted molecular weight 596 kDa and is 468% identical to Saccharomyces cerevisiae Nop5/Nop58 Immunofluorescent staining with antibodies against hNop5/Nop58 indicate that it is localized primarily to the nucleolus, and coimmunoprecipitation from nuclear extracts demonstrates that hNop5/Nop58 interacts with the box C/D family of snoRNAs Thus, hNop5/Nop58 is a common component of the box C/D snoRNPs, and joins fibrillarin as the second such component identified and characterized in metazoans
71 citations
TL;DR: Differences in the chromosomal-nucleolar junction following different fixation procedures are described and one per cent collidine-buffered OsO4 routinely produces a sharp nucleolar image with the fibrillar and ribosomal regions clearly distinguished.
71 citations