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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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Journal ArticleDOI
TL;DR: It is demonstrated that the process of nucleolar segregation and capping involves energy-dependent repositioning of nuclear proteins and RNAs and emphasize the dynamic characteristics of nuclear domain formation in response to cellular stress.
Abstract: Nucleolar segregation is observed under some physiological conditions of transcriptional arrest. This process can be mimicked by transcriptional arrest after actinomycin D treatment leading to the segregation of nucleolar components and the formation of unique structures termed nucleolar caps surrounding a central body. These nucleolar caps have been proposed to arise from the segregation of nucleolar components. We show that contrary to prevailing notion, a group of nucleoplasmic proteins, mostly RNA binding proteins, relocalized from the nucleoplasm to a specific nucleolar cap during transcriptional inhibition. For instance, an exclusively nucleoplasmic protein, the splicing factor PSF, localized to nucleolar caps under these conditions. This structure also contained pre-rRNA transcripts, but other caps contained either nucleolar proteins, PML, or Cajal body proteins and in addition nucleolar or Cajal body RNAs. In contrast to the capping of the nucleoplasmic components, nucleolar granular component proteins dispersed into the nucleoplasm, although at least two (p14/ARF and MRP RNA) were retained in the central body. The nucleolar caps are dynamic structures as determined using photobleaching and require energy for their formation. These findings demonstrate that the process of nucleolar segregation and capping involves energy-dependent repositioning of nuclear proteins and RNAs and emphasize the dynamic characteristics of nuclear domain formation in response to cellular stress.

330 citations

Journal ArticleDOI
TL;DR: It is shown that nucleolin, one of the major RNA‐binding proteins of the nucleolus, is involved in the early cleavage of pre‐rRNA, and it is demonstrated that this interaction is required for the processing reaction in vitro.
Abstract: The first processing step of precursor ribosomal RNA (pre-rRNA) involves a cleavage within the 5' external transcribed spacer. This processing requires sequences downstream of the cleavage site which are perfectly conserved among human, mouse and Xenopus and also several small nucleolar RNAs (snoRNAs): U3, U14, U17 and E3. In this study, we show that nucleolin, one of the major RNA-binding proteins of the nucleolus, is involved in the early cleavage of pre-rRNA. Nucleolin interacts with the pre-rRNA substrate, and we demonstrate that this interaction is required for the processing reaction in vitro. Furthermore, we show that nucleolin interacts with the U3 snoRNP. Increased levels of nucleolin, in the presence of the U3 snoRNA, activate the processing activity of a S100 cell extract. Our results suggest that the interaction of nucleolin with the pre-rRNA substrate might be a limiting step in the primary processing reaction. Nucleolin is the first identified metazoan proteinaceous factor that interacts directly with the rRNA substrate and that is required for the processing reaction. Potential roles for nucleolin in the primary processing reaction and in ribosome biogenesis are discussed.

322 citations

Journal ArticleDOI
TL;DR: Pulse labelling of proteins shows that NOP1 depleted strains are greatly impaired in the production of cytoplasmic ribosomes, and they have a reduced level of r RNAs and a progressive impairment of all pre‐rRNA processing steps.
Abstract: The yeast snoRNP protein, NOP1, is structurally and functionally homologous to vertebrate fibrillarin and is essential for viability. A conditionally lethal allele was constructed by placing NOP1 expression under the control of a GAL promoter. Growth on glucose medium results in the depletion of NOP1 over several generations, during which cell growth is progressively impaired. Pulse labelling of proteins shows that NOP1 depleted strains are greatly impaired in the production of cytoplasmic ribosomes, and they have a reduced level of rRNA. Northern hybridization and pulse-chase labelling of pre-rRNA show a progressive impairment of all pre-rRNA processing steps. The pathway leading to 18S rRNA is particularly affected. Methylation of pre-rRNA is concomitantly impaired and unmethylated pre-rRNA accumulates and is not processed over long periods. NOP1 depletion does not prevent the accumulation of seven snoRNAs tested including U3; the levels of two species, U14 and snR190, decline. The snoRNAs synthesized in the absence of NOP1 retain TMG cap structures. Subnuclear fractionation and immunocytochemistry indicate that they continue to be localized in the nucleolus.

319 citations

Journal ArticleDOI
TL;DR: This data provide an initial biochemical map of the pre‐40S ribosomal subunit on its path from the nucleolus to the cytoplasm, which involves fewer changes in composition than seen during 60S biogenesis.
Abstract: Recent reports have increased our knowledge of the consecutive steps during 60S ribosome biogenesis substantially, but 40S subunit formation is less well understood. Here, we investigate the maturation of nucleolar 90S pre-ribosomes into cytoplasmic 40S pre-ribosomes. During the transition from 90S to 40S particles, the majority of non-ribosomal proteins (∼30 species) dissociate, and significantly fewer factors associate with 40S pre-ribosomes. Notably, some of these components are part of both early 90S and intermediate 40S pre-particles in the nucleolus (e.g. Enp1p, Dim1p and Rrp12p), whereas others (e.g. Rio2p and Nob1p) are found mainly on late cytoplasmic pre-40S subunits. Finally, temperature-sensitive mutants mapping either in earlier (enp1-1) or later (rio2-1) components exhibit defects in the formation and nuclear export of pre-40S subunits. Our data provide an initial biochemical map of the pre-40S ribosomal subunit on its path from the nucleolus to the cytoplasm. This pathway involves fewer changes in composition than seen during 60S biogenesis.

317 citations

Journal ArticleDOI
TL;DR: The relationship of PCNA to proliferation and blast transformation may be associated with events related to DNA synthesis in these cells and the autoantibody was used as a reagent to determine the distribution.
Abstract: A nuclear antigen associated with cell proliferation (proliferating cell nuclear antigen-PCNA) and blast transformation is recognized by autoantibodies in the sera of some patients with systemic lupus erythematosus This autoantibody is a precipitating antibody and also reacts in immunofluorescence, staining the nucleoplasm of proliferating and blast-transformed cells The autoantibody was used as a reagent to determine the distribution of PCNA in a synchronized continuous B lymphoid cell line (WiL-2) and in mitogen-induced blast-transformed lymphocytes In WiL-2 cells, PCNA was detected as speckled nucleoplasmic staining in G1, S, and G2 phases of the cell cycle In addition, during late G1 and early S phases, PCNA was also detected in the nucleolus During mitogen-induced blast transformation of lymphocytes, PCNA was noticed in the nucleolus before the initiation of DNA synthesis and later became nucleoplasmic with disappearance of nucleolar staining These studies demonstrate that the relationship of PCNA to proliferation and blast transformation may be associated with events related to DNA synthesis in these cells

312 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023145
2022209
2021143
2020125
2019139
2018121