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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: During post-mitotic reformation and nucleogenesis there is a progressive decline in the fraction of specific satellite regions of DNA that remain associated with pKi-67, which may be relevant to nucleolar reformation following mitosis.
Abstract: pKi-67 is a nucleolar antigen that provides a specific marker for proliferating cells. It has been shown previously that pKi-67's distribution varies in a cell cycle-dependent manner: it coats all chromosomes during mitosis, accumulates in nuclear foci during G1 phase (type I distribution) and localizes within nucleoli in late G1 S and G2 phase (type II distribution). Although no function has as yet been ascribed to pKi-67, it has been found associated with centromeres in G1. In the present study the distribution pattern of pKi-67 during G1 in human dermal fibroblasts (HDFs) was analysed in more detail. Synchronization experiments show that in very early G1 cells pKi-67 coincides with virtually all satellite regions analysed, i.e. with centromeric (alpha-satellite), telomeric (minisatellite) and heterochromatic blocks (satellite III) on chromosomes 1 and Y (type Ia distribution). In contrast, later in the G1 phase, a smaller fraction of satellite DNA regions are found collocalized with pKi-67 foci (type Ib distribution). When all pKi-67 becomes localized within nucleoli, even fewer satellite regions remain associated with the pKi-67 staining. However, all centromeric and short arm regions of the acrocentric chromosomes, which are in very close proximity to or even contain the rRNA genes, are collocalized with anti-pKi-67 staining throughout the remaining interphase of the cell cycle. Thus, our data demonstrate that during post-mitotic reformation and nucleogenesis there is a progressive decline in the fraction of specific satellite regions of DNA that remain associated with pKi-67. This may be relevant to nucleolar reformation following mitosis.

111 citations

Journal ArticleDOI
TL;DR: Ribonucleoprotein particles containing the precursors of ribosomal RNA were extracted from L cell nucleoli and analyzed under conditions comparable to those used in the characterization of cytoplasmic ribosomes, suggesting that the precursor particles have a relatively higher ratio of protein to RNA, and that ribosome maturation involves a progressive decrease in the proportion of associated protein.
Abstract: Ribonucleoprotein (RNP) particles containing the precursors of ribosomal RNA were extracted from L cell nucleoli and analyzed under conditions comparable to those used in the characterization of cytoplasmic ribosomes. Using nucleoli from cells suitably labeled with 3H-uridine, we detected three basic RNP components, sedimenting at approximately 62S, 78S, and 110S in sucrose gradients containing magnesium. A fourth particle, sedimenting at about 95S, appears to be a dimer of the 62S and 78S components. When centrifuged in gradients containing EDTA, the 62S, 78S, and 110S particles sediment at about 55S, 65S, and 80S, respectively. RNA was extracted from RNP particles which were prepared by two cycles of zonal centrifugation. The 62S particles yielded 32S RNA and a detectable amount of 28S RNA, the 78S structures, 32S RNA and possibly some 36S RNA, and the 110S particles, a mixture of 45S, 36S, and 32S RNA's. When cells were pulsed briefly and further incubated in the presence of actinomycin D, there was a gradual shift of radioactivity from heavier to lighter particles. This observation is consistent with the scheme of maturation: 110S → 78S → 62S. The principal buoyant densities in cesium chloride of the 110S, 78S, and 62S particles are 1.465, 1.490, and 1.545, respectively. These densities are all significantly lower than 1.570, which is characteristic of the mature large subunit of cytoplasmic ribosomes, suggesting that the precursor particles have a relatively higher ratio of protein to RNA, and that ribosome maturation involves, in addition to decrease in the size of the RNA molecules, a progressive decrease in the proportion of associated protein.

111 citations

Journal ArticleDOI
01 Sep 2001-RNA
TL;DR: The results indicate that Bms1p may act as a molecular switch during maturation of the 40S ribosomal subunit in the nucleolus, and it is demonstrated that mutations of amino acids implicated in GTP/GDP binding affect BMS1p activity in vivo.
Abstract: Maturation of 18S rRNA and biogenesis of the 40S ribosomes in yeast requires a large number of trans-acting factors, including the U3 small nucleolar ribonucleoprotein (U3 snoRNP), and the recently characterized cyclase-like protein Rcl1p. U3 snoRNP is a key particle orchestrating early 35S rRNA cleavage events. A unique property of Rcl1p is that it specifically associates with U3 snoRNP, but this association appears to occur only at the level of nascent ribosomes and not with the U3 monoparticle. Here we report the characterization of Bms1p, a protein that associates with Rcl1p in multiple structures, including a specific complex sedimenting at around 10S. Like Rcl1p, Bms1p is an essential, evolutionarily conserved, nucleolar protein, and its depletion interferes with processing of the 35S pre-rRNA at sites A0, A1, and A2, and the formation of 40S subunits. The N-terminal domain of Bms1p has structural features found in regulatory GTPases and we demonstrate that mutations of amino acids implicated in GTP/GDP binding affect Bms1p activity in vivo. The results indicate that Bms1p may act as a molecular switch during maturation of the 40S ribosomal subunit in the nucleolus.

111 citations

Journal ArticleDOI
TL;DR: The ribosomal protein L23 is identified as a negative regulator of Miz1-dependent transactivation, which may provide a feedback mechanism that links translation of Myc target genes and cell growth to Miz 1-dependent cell-cycle arrest.
Abstract: The Myc-associated zinc-finger protein, Miz1, is a negative regulator of cell proliferation and induces expression of the cell-cycle inhibitors p15(Ink4b) and p21(Cip1). Here we identify the ribosomal protein L23 as a negative regulator of Miz1-dependent transactivation. L23 exerts this function by retaining nucleophosmin, an essential co-activator of Miz1 required for Miz1-induced cell-cycle arrest, in the nucleolus. Mutant forms of nucleophosmin found in acute myeloid leukaemia fail to co-activate Miz1 and re-localize it to the cytosol. As L23 is encoded by a direct target gene of Myc, this regulatory circuit may provide a feedback mechanism that links translation of Myc target genes and cell growth to Miz1-dependent cell-cycle arrest.

111 citations

Journal ArticleDOI
TL;DR: A large decrease in the transcription rates by RNA polymerases I and II is shown when proliferative forms of Trypanosoma cruzi transform into non-proliferative and infective forms (trypomastigotes) and these changes in transcription occur in parallel with modifications in the nuclear structure.

111 citations


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