Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nucleotide sequences of intracellular Epstein-Barr viral DNAs in tumor biopsy cells of clones independently transformed in vitro were generally compared by determing the electrophoretic mobilities of restriction endonuclease cleavage fragments of the viral DNA. To carry out this comparison, cleaved cell DNAs were electrophoresed in agarose gels and transferred to nitrocellulose paper, and the immobilized viral species were identified by hybridization with purified, viral DNA labeled in vitro. These studies lead to three findings: (i) The complexities of all of the intracellular viral DNAs are similar to one another and to that of purified virion DNA. (II) There are small differences in the cleavage patterns of some viral DNAs, but the differences of the cleavage patterns of the viral DNA resident in the tumor cells and in the cells transformed in vitro are not more pronounced than those found between the different clones of the cells transformed in vitro. (iii) All of the viral DNA species contain a repeated sequence. The first two conclusions indicate that the Epstein-Barr virus strain studied in the laboratory appears indistinguishable from that associated with Burkitt lymphoma.
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PMID:Comparison of Epstein-Barr viral DNAs in Burkitt lymphoma biopsy cells and in cells clonally transformed in vitro. 20 Sep 25

RNA was extracted from the Burkitt lymphoma-derived cell line Raji and from Burkitt lymphoma tumor biopsies, isotope labeled in vitro by iodination with 125I, and hybridized to electrophoretically separated restriction endonuclease fragments of Epstein-Barr virus DNA on nitrocellulose membranes. The results indicated that only certain parts of the Epstein-Barr virus genome are represented as polyribosomal RNA in Raji cells, with a pronounced dominance of RNA sequences complementary to a 2.0 x 10(6)-dalton segment of Epstein-Barr virus DNA located close to the left end of the viral genome. A map of virus-specific polyribosomal RNA sequences was constructed, which indicated that a minimum of three regions of the Epstein-Barr virus genome are expressed in Raji cells. Total-cell RNA preparations from five Burkitt lymphoma biopsies contained RNA sequences homologous to the same regions of Epstein-Barr virus DNA as polyribosomal RNA from Raji cells, albeit at different relative proportions.
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PMID:Identification of transcribed regions of Epstein-Barr virus DNA in Burkitt lymphoma-derived cells. 23 90

Epstein-Barr virus (EBV) nuclear antigen (EBNA) was purified from the Burkitt lymphoma line Raji and its EBV DNA-binding properties were characterized. EBNA binding protected fragments of about 30 bp of B95-8 cell-derived EBV DNA from an excess of DNase I. Human anti-EBNA antibodies prevented DNA binding. Purified extracts from EBNA-negative cells did not protect EBV DNA against DNase I digestion. Mapping of the EBV DNA fragments protected from endonuclease (EcoRI, HindIII, SalI) digestion revealed many binding sites. Similar results were obtained following mixing of crude cell extracts and HindIII-digested fragments of EBV DNA and subsequent immunoprecipitation of the EBNA-DNA complex. In experiments involving the analysis of EBV DNA, fragments were protected from DNase I digestion by purified EBNA.
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PMID:Interaction between Epstein-Barr virus-determined nuclear antigen (EBNA) and the viral DNA. 609 16

A comparative analysis of three Epstein-Barr virus DNAs from American patients with infectious mononucleosis (B95-8, Cherry, and Lamont) and four Epstein-Barr virus DNAs from African patients with Burkitt lymphoma (AG876, W91, Raji, and P3HR-1) indicated that the usual format of Epstein-Barr virus DNA includes a variable number of direct repeats of a 0.35 X 10(6)-dalton sequence (TR) at both ends of the DNA, a 9 X 10(6)-dalton sequence of largely unique DNA (Us), a variable number of repeats of a 2 X 10(6)-dalton sequence (IR), and a 89 X 10(6)-dalton sequence of largely unique DNA (UL). Within UL there was homology between DNA at 26 X 10(6) to 28 X 10(6) daltons and DNA at 93 X 10(6) to 95 X 10(6) daltons. The relative sequence order (TR, US, IR, UL, TR) did not vary among "standard" Epstein-Barr virus DNA molecules of each isolate. B95-8 DNA had an unusual deletion extending from 91 X 10(6) to 100 X 10(6) daltons, and P3HR-1 DNA had an unusual deletion extending from 23.5 X 10(6) to 26 X 10(6) daltons. There was sufficient variability among the EcoRI and BamHI fragments of the DNAs to identify each isolate specifically. However, we discerned no distinguishing features for the two geographic or pathogenic origins of the seven isolates. Three intracellular DNAs (Raji, Lamont, and Cherry) and one virion DNA (P3HR-1) were heterogenous in molecular organization and had subpopulations of rearranged or defective molecules. Some regions, particularly 59 X 10(6) to 63 X 10(6) daltons and sequences around TR, frequently participated in rearrangements. Restriction endonuclease maps of the standard and rearranged DNAs of the seven isolates are presented.
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PMID:Epstein-Barr virus DNA. IX. Variation among viral DNAs from producer and nonproducer infected cells. 626 34

Cytoplasmic RNA prepared from five lymphoid cell lines and a Burkitt lymphoma biopsy was radioactively labeled in vitro and hybridized to cloned EcoRI restriction endonuclease fragments of B95-8 Epstein-Barr virus DNA. The results confirmed that the most abundant cytoplasmic RNA species in such cells is specified by a small region of the genome defined by the EcoRI J fragment. Detailed mapping experiments precisely localized these transcripts within the sequence of the rightmost one-third of the EcoRI J fragment. DNA sequencing suggested that this region of the Epstein-Barr virus genome is unable to code for protein. The major early transcripts consisted of two non-polyadenylated RNA species, each about 170 nucleotides in length. They were both transcribed off the same strand of the DNA and showed significant sequence homology with each other. The coding sequences of the two small RNAs contained potential intragenic control regions for RNA polymerase III.
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PMID:Characterization of the major Epstein-Barr virus-specific RNA in Burkitt lymphoma-derived cells. 628 55

By cloning the HR-1 Burkitt lymphoma line, we previously uncovered two distinct biological variants of nontransforming Epstein-Barr virus (EBV). The most commonly cloned variant has a low rate of spontaneous viral synthesis and is unable to induce early antigen in Raji cells (EAI-). A rare variant spontaneously releases virus which is capable of inducing early antigen in Raji cells (EAI+). Since EAI- virus lacks heterogeneous DNA (het-) and EAI+ virus contains heterogeneous DNA (het+), we suggested that spontaneous viral synthesis and induction of early antigen are biological properties which correlate with the presence of het sequences. The present experiments provide three new lines of experimental evidence in favor of this hypothesis. (i) Revertant subclones of the EAI+ het+ variant which have lost the het DNA concomitantly lost EAI ability. Thus, het DNA is not stably associated with the cells as are the episomes. (ii) het DNA was acquired by two het- subclones of the HR-1 line after superinfection with EAI+ virus. After superinfection, these clones synthesized EAI+ het+ virus. Thus, het DNA may be maintained in the HR-1 line by cell-to-cell spread. (iii) Virus with het DNA activated full expression of endogenous latent EBV of the transforming phenotype in a line of immortalized neonatal lymphocytes designated X50-7. By use of restriction endonuclease polymorphisms unique to both the superinfecting and endogenous genomes, we show that the genome of the activated virus resembles that of the virus which was endogenous to X50-7 cells. This result suggests that het sequences result in transactivation of the latent EBV. het DNA had homology with EBV sequences which are not normally contiguous on the physical map of the genome. het DNA was always accompanied by the presence of DNA of nonheterogenous HR-1. Thus, het DNA is a form of "defective" EBV DNA. However, the biological effect of this defective DNA is to enhance rather than to interfere with EBV replication. This is a novel property of defective virus.
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PMID:Epstein-Barr virus with heterogeneous DNA disrupts latency. 632 89

The state of B cell maturation profoundly influences the outcome, i.e., activation, growth arrest, or programmed cell death, of a variety of stimuli, including the calcium ionophore, ionomycin. Initial studies confirmed the observation that cell lines representative of immature B cells, i.e., Burkitt lymphoma cell lines, were induced to undergo apoptosis in response to ionomycin, whereas more mature B cell lines did not, and instead underwent cell cycle arrest in the G1 interval. To understand this differential outcome, we have focused on comparing the expression and activation of an endonuclease(s) in cells induced by ionomycin to undergo programmed cell death (Ramos) with cells resistant to ionomycin-induced programmed cell death (Ly1). Our results demonstrated that a low m.w. fraction of an endogenous Ca2+/Mg(2+)-dependent endonuclease was activated in Ramos cells, but not in activated Ly1 cells, following the addition of ionomycin. Of interest, however, low m.w. endogenous endonuclease(s) activity was induced when isolated Ly1 cell nuclei were treated with exogenous calcium instead. Use of field inversion gel electrophoresis further indicated that cleavage of DNA into large m.w. (> 50 kbp) DNA fragments does not precede ionomycin-induced internucleosomal cleavage in Ramos cells or in ionomycin-resistant Ly1 cells. In summary, these data support the conclusion that ionomycin-induced apoptosis involves the activation of a latent, low m.w., calcium-responsive endonuclease and suggest that control of endonuclease depression may contribute to cell-specific regulation of calcium ionophore-induced apoptosis.
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PMID:Differential activation of a calcium-dependent endonuclease in human B lymphocytes. Role in ionomycin-induced apoptosis. 756 Oct 22

Apoptosis, or programmed cell death, is a general mechanism for removal of unwanted cells from the immune system. It is characterized by chromatin condensation, a reduction in cell volume, and endonuclease cleavage of DNA into oligonucleosomal length fragments. Apoptosis is also accompanied by a loss of membrane phospholipid asymmetry, resulting in the exposure of phosphatidylserine at the surface of the cell. Expression of phosphatidylserine at the cell surface plays an important role in the recognition and removal of apoptotic cells by macrophages. Here we describe a new method for the detection of apoptotic cells by flow cytometry, using the binding of fluorescein isothiocyanate-labeled annexin V to phosphatidylserine. When Burkitt lymphoma cell lines and freshly isolated germinal center B cells are cultured under apoptosis inducing conditions, all cells showing chromatin condensation strongly stain with annexin V, whereas normal cells are annexin V negative. Moreover, DNA fragmentation is only found in the annexin V-positive cells. The nonvital dye ethidium bromide was found to stain a subpopulation of the annexin V-positive apoptotic cells, increasing with time. Our results indicate that the phase in apoptosis that is characterized by chromatin condensation coincides with phosphatidylserine exposure. Importantly, it precedes membrane damage that might lead to release from the cells of enzymes that are harmful to the surrounding tissues. Annexin V may prove important in further unravelling the regulation of apoptosis.
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PMID:Annexin V for flow cytometric detection of phosphatidylserine expression on B cells undergoing apoptosis. 806 38