Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examined the mobilities of nucleolar components that act at various steps of the ribosome biogenesis pathway. Fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) analyses demonstrate that factors involved in rRNA transcription (upstream-binding factor [UBF]), processing (nucleolin, fibrillarin, and RNase MRP subunits, Rpp29), and ribosome assembly (B23) exchange rapidly between the nucleoplasm and nucleolus. In contrast, the mobilities of ribosomal subunit proteins (S5, L9) are much slower. Selective inhibition of RNA polymerase I transcription does not prevent the exchanges but influences the rates of exchange differentially for different nucleolar components. These findings suggest that the rapid exchange of nucleolar components between the nucleolus and nucleoplasm may represent a new level of regulation for rRNA synthesis. The different dynamic properties of proteins involved in different steps of ribosome biogenesis imply that the nucleolar association of these proteins is due to their specific functional roles rather than simply their specific nucleolar-targeting events.
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PMID:Nucleolar components involved in ribosome biogenesis cycle between the nucleolus and nucleoplasm in interphase cells. 1128 83

Cell death in eukaryotes can occur by either apoptosis or necrosis. Apoptosis is characterized by well-defined nuclear changes which are thought to be the consequence of both proteolysis and DNA fragmentation. On the other hand, the nuclear modifications that occur during necrosis are largely less known. Here, we have investigated whether or not nuclear modifications occur during ethanol-induced necrotic cell death of HL-60 cells. By means of immunofluorescence staining, we demonstrate that the patterns given by antibodies directed against some nuclear proteins (lamin B1, NuMA, topoisomerase IIalpha, SC-35, B23/nucleophosmin) changed in necrotic cells. The changes in the spatial distribution of NuMA strongly resembled those described to occur during apoptosis. On the contrary, the fluorescent pattern characteristic for other nuclear proteins (C23/nucleolin, UBF, fibrillarin, RNA polymerase I) did not change during necrosis. By immunoblotting analysis, we observed that some nuclear proteins (SAF-A, SATB1, NuMA) were cleaved during necrosis, and in the case of SATB1, the apoptotic signature fragment of 70 kDa was also present to the same extent in necrotic samples. Caspase inhibitors did not prevent proteolytic cleavage of the aforementioned polypeptides during necrosis, while they were effective if apoptosis was induced. In contrast, lamin B1 and topoisomerase IIalpha were uncleaved in necrotic cells, whereas they were proteolyzed during apoptosis. Transmission electron microscopy analysis revealed that slight morphological changes were present in the nuclear matrix fraction prepared from necrotic cells. However, these modifications (mainly consisting of a rarefaction of the inner fibrogranular network) were not as striking as those we have previously described in apoptotic HL-60 cells. Taken together, our results indicate that during necrosis marked biochemical and morphological changes do occur at the nuclear level. These alterations are quite distinct from those known to take place during apoptosis. Our results identify additional biochemical and morphological criteria that could be used to discriminate between the two types of cell death. J. Cell. Biochem. Suppl. 36: 19-31, 2001.
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PMID:Nuclear changes in necrotic HL-60 cells. 1145 67

The nuclear functions in erythrocytes are almost completely extinct. There is no RNA polymerase I transcription, although a remnant nucleolar structure is still present. The remnant nucleolus of Xenopus laevis erythrocytes maintains a morphologically organized structure, nearly exclusively fibrillar. In this inactive nucleolar remnant, we revealed the presence of a modified form of transcription factor UBF. Several proteins of the processing machinery such as fibrillarin, nucleolin and B23/NO38, snoRNAs U3 and U8, and partially processed preribosomal RNAs colocalized in these remnant structures. Attempts to reprogram these erythrocyte nuclei in Xenopus egg extract showed that import of several nucleolar proteins was induced while the nucleolar remnant was disorganized. UBF became abundant and showed a necklace-like distribution on the decondensed ribosomal genes. Fibrillarin, nucleolin, and snoRNAs U3 and U8, also largely imported from the extract, were associated in large prenuclear bodies scattered in the nucleoplasm. B23/NO38 was present in different small bodies formed only in the most decondensed nuclei. In these remodeled erythrocyte nuclei, there was no imported preribosomal RNA and the initial presence of a residual nucleolar structure containing several partners of ribosome biogenesis was not sufficient to promote reassembly of newly imported nucleolar machineries. These nuclei, which reproduce the early events of nucleogenesis are also transcriptionally silent and thus compare to the early embryonic nuclei of Xenopus laevis.
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PMID:Maintenance of nucleolar machineries and pre-rRNAs in remnant nucleolus of erythrocyte nuclei and remodeling in Xenopus egg extracts. 1152 36

In the present study immunofluorescence confocal laser scanning microscopy, autoradiography following (3)H-uridine incubation and transmission electron microscopy were used to evaluate the nucleolar protein localization, transcriptional activity, and nucleolar ultrastructure during genomic re-programming in bovine embryos reconstructed by nuclear transfer from granulosa cells into non-activated cytoplasts followed by activation. During the 1st cell cycle (1-cell embryos), no autoradiographic labelling was detected. Ultrastructurally, nucleoli devoid of a granular component were observed. During the 2nd cell cycle (2-cell embryos) autoradiographic labelling was also lacking and the embryos displayed varying degrees of nucleolar inactivation. During both the 3rd (4-cell embryos) and 4th (tentative 8-cell embryos), cell cycles autoradiographic labelling was lacking in some embryos, while others displayed labelling and associated formation of fibrillo-granular nucleoli. During the 5th cell cycle (tentative 16-cell embryos), all embryos displayed autoradiographic labelling and fibrillo-granular nucleoli. In some blastomeres, however, deviant nucleolar ultrastructure was observed. During the first cell cycle labelling of RNA polymerase I, fibrillarin, upstream binding factor (UBF) and nucleolin (C23) was localized to nuclear entities. During the 2nd cell cycle, only labelling of RNA polymerase I and fibrillarin persisted. During the 3rd and 4th cell cycle labelling of fibrillarin persisted, labelling of nucleophosmin (B23) appeared and that of nucleolin re-appeared. During the 5th cell cycle almost all embryos showed complete labelling of all proteins except for UBF, which lacked in more than half of the embryos. In conclusion, bovine granulosa cell nuclear transfer embryos showed re-modelling of the nucleoli to an inactive form followed by re-formation of fibrillo-granular nucleoli. The re-formation of fibrillo-granular nucleoli was initiated already during the 3rd cell cycle, which is one cell cycle earlier than in in vivo- and in vitro-derived bovine embryos. Moreover, in more than half of the embryos, UBF could not be immunocytochemically localized to the nucleolar compartment during the 5th cell cycle indicating lack of developmental potentials.
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PMID:Nucleolar protein allocation and ultrastructure in bovine embryos produced by nuclear transfer from granulosa cells. 1189 19

In the present study, immunofluorescence confocal laser scanning microscopy, autoradiography following (3)H-uridine incubation, and transmission electron microscopy were used to evaluate the nucleolar protein localization, transcriptional activity, and nucleolar ultrastructure during genomic reprogramming in bovine embryos reconstructed by nuclear transfer from in vitro-produced bovine morulae to activated cytoplasts. During the first cell cycle (one-cell embryos), no autoradiographic labelling was detected. Ultrastructurally, whorls consisting of densely packed fibrillar material were observed instead of nucleoli. During the second, third, and fourth cell cycle (two-, four-, and tentative eight-cell embryos), autoradiographically unlabelled nuclei contained vacuolated bodies consisting of densely packed fibrillar material. Also, during the fourth cell cycle, the first nucleoplasmic autoradiographic labelling was observed, but still without formation of fibrillo-granular nucleoli. During the fifth cell cycle (tentative 16-cell embryos), the nuclei displayed autoradiographic labelling over both nucleoplasm and presumptive nucleoli, and the formation of fibrillo-granular nucleoli was observed. In a certain proportion of blastomeres, however, abnormal patterns of nucleolar formation and apoptosis were noted. During the first two cell cycles, labelling of RNA polymerase I, fibrillarin, upstream binding factor (UBF), nucleolin (C23), and nucleophosmin (B23) was localized to nuclear entities. During the third cell cycle, labelling of topoisomerase I was observed in addition. During the fourth and fifth cell cycles, a substantial portion of the embryos presented blastomeres that lacked labelling of several of these nucleolar proteins. In conclusion, the nuclear transfer procedure was associated with remodelling of the nucleoli to an inactive form, followed by reformation of fibrillo-granular nucleoli during the fifth cell cycle. Moreover, a certain proportion of blastomeres failed to form functional nucleoli with respect to both ultrastructural organization and protein allocation.
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PMID:Nucleolar protein allocation and ultrastructure in bovine embryos produced by nuclear transfer from embryonic cells. 1190 Jun 41

The nucleolus is the site of ribosome biosynthesis, but is now known to have other functions as well. In the present study we have investigated how the distribution of signal recognition particle (SRP) RNA within the nucleolus relates to the known sites of ribosomal RNA synthesis, processing, and nascent ribosome assembly (i.e., the fibrillar centers, the dense fibrillar component (DFC), and the granular component). Very little SRP RNA was detected in fibrillar centers or the DFC of the nucleolus, as defined by the RNA polymerase I-specific upstream binding factor and the protein fibrillarin, respectively. Some SRP RNA was present in the granular component, as marked by the protein B23, indicating a possible interaction with ribosomal subunits at a later stage of maturation. However, a substantial portion of SRP RNA was also detected in regions of the nucleolus where neither B23, UBF, or fibrillarin were concentrated. Dual probe in situ hybridization experiments confirmed that a significant fraction of nucleolar SRP RNA was not spatially coincident with 28S ribosomal RNA. These results demonstrate that SRP RNA concentrates in an intranucleolar location other than the classical stations of ribosome biosynthesis, suggesting that there may be nucleolar regions that are specialized for other functions.
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PMID:Signal recognition particle RNA localization within the nucleolus differs from the classical sites of ribosome synthesis. 1242 65

After fertilization, ribosomal RNA synthesis is silenced during a period which depends on the species. Data concerning the reassembly of a functional nucleolus remain scarce. We have examined by immunocytochemistry, Western blots, and BrUTP microinjection the dynamics of major nucleolar proteins during the first cycles of mouse embryogenesis, in relation to rDNA transcription sites and coilin, a marker of Cajal bodies. We show that: (1) the reinitiation of rDNA transcription occurs at the two-cell stage, 44-45 h after hCG injection (hphCG), at the surface of the nucleolar precursor bodies (NPBs), where the RNA polymerase I (pol I) transcription complex is recruited 4-5 h before; (2) the NPBs are not equal in their ability to support recruitment of pol I and rDNA transcription; (3) maternally inherited fibrillarin undergoes a dynamic redistribution during the second cell stage, together with coilin, leading to the assembly of the Cajal body around 40 hphCG; and (4) the pol I complex is first recruited to the Cajal body before reaching its rDNA template. We also find that fibrillarin and B23 are both directly assembled around NPBs prior to ongoing pre-rRNA synthesis. Altogether, our results reveal a role of the Cajal bodies in the building of a functional nucleolus.
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PMID:The step-wise assembly of a functional nucleolus in preimplantation mouse embryos involves the cajal (coiled) body. 1249 Jan 98

The aim of this study was to describe the dynamic changes in the localization of the key nucleolar protein markers, fibrillarin, B23/nucleophosmin, C23/nucleolin, protein Nopp140, during the final stages of bovine oocyte growth. All these proteins were present in the large reticulated nucleoli of oocytes from the small-size category follicles (<1 mm). The entire nucleolus exhibited strong positivity for UBF (upstream binding factor, RNA polymerase I-specific transcription initiation factor), which displayed a dotted staining pattern. In contrast, protein p130 was diffusely distributed throughout the nucleus and excluded from nucleoli. In oocytes approaching the late period of growth (2-3-mm follicles), UBF localization shifted to the nucleolar periphery. Double staining of UBF-p130 revealed a gradual accumulation of p130 at the periphery shell around the nucleolus. In fully grown oocytes (>3-mm follicles), all studied nucleolar proteins were detected in the small compact nucleoli. The cap structure, attached to the compact nucleolus surface, was positive for UBF and PAF53 (subunit of RNA polymerase I). The UBF-positive cap showed a close structural association with p130. It is concluded that, during the process of oocyte nucleolus compaction, UBF and PAF53, proteins involved in the rDNA transcription, are segregated from fibrillarin and Nopp140, proteins essential for early steps of pre-rRNA processing. The observed changes may reflect the transition from pre-rRNA synthesis to pre-rRNA processing as an analysis of the relative abundance of the developmentally important gene transcripts confirmed. In addition, discovered structural association between UBF and p130 suggests a role for pocket proteins in ribosomal gene silencing in mammalian oocytes.
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PMID:Immunolocalization of upstream binding factor and pocket protein p130 during final stages of bovine oocyte growth. 1461 6

The soluble fraction of nuclear proteins is a functionally significant fraction, since it has been shown that it contains ribonucleoproteins active in nuclear RNA metabolism. The aim of this work was to detect variations associated with cell proliferation, by comparing two-dimensional proteomes obtained from the soluble fractions of onion nuclei isolated from actively proliferating root meristematic cells versus nonmeristematic root cells. In particular, we have studied the physicochemical features of the major nucleolar protein NopA100, a highly phosphorylated, nucleolin-like protein. A total of 384 spots were quantified in meristematic nuclei, while only 209 were detected in nonmeristematic nuclei. The comparison of both proteomes resulted in the determination of specific spots for each proliferative state and those which were common to both cases. Furthermore, among these latter, we could discriminate quantitative differences. Interestingly, well-known nucleolar proteins, such as RNA polymerase I, B23 and the nucleolin-like protein NopA100, were significantly increased in proliferating cells. Western blots with anti-NopA100 antibody demonstrated 26 spots in the meristematic sample. All the spots detected were clustered at 100 kDa and were distributed through an isoelectric point (pI) range of 4.3-6.6. In contrast, only seven spots were found in the extract from nonmeristematic nuclei, and the pI range was shortened to 4.8-6.1. These results indicate that the state of NopA100 phosphorylation correlates with the degree of nucleolar activity, i.e. the protein is more highly phosphorylated in cycling cells. We have also analyzed the bidimensional silver staining of the nucleolar organizing region (Ag-NOR) pattern of the soluble nuclear fraction in order to identify plant cell phosphoproteins that are considered to be markers of proliferation. These experiments demonstrated that NopA100, the onion, nucleolin-like protein, is an Ag-NOR protein. In addition we found that the plant homologue of the vertebrate nucleolar phosphoprotein B23 migrated as two clusters of acidic spots, 43 and 42 kDa respectively in molecular mass. The differences between these features and those described for mammalian cells is discussed. Our results demonstrate that the use of protein fractionation procedures with functional significance and the location of candidate spots by indirect techniques are advantageous, complementary methods to random selection procedures for proteomic studies involving further mass spectrometry analysis.
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PMID:Identification of specific plant nucleolar phosphoproteins in a functional proteomic analysis. 1476 Jul 10

Scleroderma is an autoimmune disease involving endothelial cell damage and fibroblast overproduction of extracellular matrix. Several autoantibodies present in the sera of patients with scleroderma, including anti-endothelial cell, antifibroblast, anti-matrix metalloproteinase, and antifibrillin-1 antibodies, may directly contribute to disease pathogenesis. Scleroderma also is characterized by the presence of antinuclear and antinucleolar antibodies, which correlate with particular phenotypes. These include antitopoisomerase-I, anticentromere, antihistone, anti-polymyositis/scleroderma, anti-Th/To, anti-U3-small nucleolar ribonucleoprotein particle, anti-U1-small nuclear ribonucleoprotein particle, anti-RNA polymerase, and anti-B23 antibodies. Other antibodies classically associated with other autoimmune diseases, such as antiphospholipid, antineutrophil cytoplasmic, and antimitochondrial antibodies, also have been described in patients with scleroderma. This review will summarize the various autoantibodies associated with scleroderma, their putative pathogenic roles, and their phenotypic correlations.
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PMID:Antibodies in scleroderma: direct pathogenicity and phenotypic associations. 1501 47


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