Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.31.1 (micrococcal nuclease)
 2,818 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chromatin fragments released from intact Friend erythroleukemia cell nuclei during limited incubation with micrococcal nuclease, DNase II or DNase I were analyzed to determine the distribution of DNA methyltransferase in chromatin. The enzyme was released in a free form when internucleosomal DNA was digested with micrococcal nuclease but was found associated with Mg++-precipitable polynucleosomes after DNase II digestion. Less than 25% of the enzyme was released from nuclei incubated with DNase I under conditions where transcriptionally active chromatin should have been completely digested. These results indicated that the bulk of DNA methyltransferase was bound to "linker" DNA in condensed regions of chromatin. Preferential rebinding of free enzyme to linker DNA was also demonstrated in vitro. The possibility that chromatin proteins play a role in regulating access of DNA methyltransferase to specific sites in DNA is discussed in light of these findings.
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PMID:Localization of DNA methyltransferase in the chromatin of Friend erythroleukemia cells. 627 20

The pulse-chase experiments with Friend erythroleukemia cells designed to reveal the metabolic properties of the protein complex of 40-S particles showed that the major polypeptides of this complex turn over with half-lives between 19 h and 206 h. the main conclusion from the experiments is that the complex does not degrade as a single unit. Since the individual polypeptides forming the complex live much longer than hnRNA, and in addition degrade at a different rate, we considered the following two modes of degradation as most likely. (1) The complex might not be subjected to a profound degradation at the end of the processing of associated pre-mRNA. In this case it should exist as a long-lived recyclable mosaic of metabolically differing polypeptides whose replacement takes place at a specific rate. (2) Alternatively, the protein complex might be completely degraded at the end of processing, but in a way that liberates free individual polypeptides available for recycling. The further experiments indicate that the 37 000-Mr, 34 000-Mr and 32 000-Mr core proteins in isolated 40-S particles and in particles associated with a nuclear fraction released from chromatin after micrococcal nuclease digestion degrade at different rates. These experiments suggest the existence of at least a metabolic heterogeneity among the population of nuclear particles carrying pre-mRNA.
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PMID:Turnover of the major polypeptides of 40-S monomer particles. 721 42

The influence of cytosol proteins on the replication of DNA and chromatin in isolated nuclei from Friend erythroleukemia cells has been investigated. The overall process has been clearly shown to proceed stepwise. In the absence of cytosol proteins DNA chain growth tends to stop after the addition of approximately 200 nucleotides to the ends of growing chains. In the presence of cytosol proteins these sections grow to approximately 250 nucleotides, and participate in the stepwise extension of the replication process through adjacent nucleosomal sections of the template. Immediately following pulse labeling, the newly replicated DNA resides in a chromatin form which appears to be relatively resistant to digestion by micrococcal nuclease. During a chase interval, the association of the pulse-labeled DNA with nuclear proteins matures to a form which yields lengths of DNA upon digestion with micrococcal nuclease that correspond to mono-, di-, tri- and polynucleosomal units of chromatin. In the absence of cytosol proteins the nuclease resistant state of the labeled DNA tends to predominate and persist. The data support the view that DNA replication in a chromosomal setting proceeds stepwise over successive nucleosomal sections of template made accessible by the interaction of the cytosol proteins at or near the replication fork.
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PMID:Role of cytosol proteins in DNA chain growth and chromatin replication in Friend erythroleukemia cell nuclei. 724 97

The chromatin structure of morphologically-similar, but increasingly-malignant erythroleukemia cells was investigated using milk micrococcal nuclease digestion of isolated nuclei. The maximum solubilization of chromatin was unique for each of the three cell types: the least malignant (our Stage II) released 61% of its chromatin DNA, the most malignant (Stage IV), 46%, and the intermediate (Stage III) released 36%. An analysis of the nucleosome oligomers liberated by digestion also demonstrated differences. After 15 minutes of digestion when release was reaching its maximum, a greater proportion of large nucleosomal oligomers (sizes > trinucleosome) was released from Stage II nuclei than from Stage III or IV nuclei. The cell types also differed in the relative amount of H1-depleted mononucleosomes released. Analysis of the size of the double-stranded DNA associated with mononucleosomal particles showed that Stage III mononucleosomes were smaller (148 bp) than Stage IV (167 bp) or Stage II (190 bp). In addition, while the DNA of mononucleosomes depleted in H1 was smaller than that in the H1-containing species, relative size differences among the different cell types were retained. These data suggested that the difference in the mononuocleosome particle size resistant to nuclease digestion was independent of histone H1. Differences in nucleosome repeat length were also noted among the cell types. These studies have demonstrated dramatic differences in chromatin structure associated with malignant potential of an otherwise morphologically identical cell type. These findings may reflect changes in the relative amounts of H2a variants which we have previously described among the different malignant cell types.
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PMID:Organizational changes in chromatin at different malignant stages of Friend erythroleukemia. 746 15

The beta-like globin genes require the upstream locus control region (LCR) for proper expression. The active elements of the LCR coincide with strong erythroid-specific DNase I-hypersensitive sites (HSs). We have used 5' HS4 as a model to study the formation of these HSs. Previously, we identified a 101 bp element that is required for the formation of this HS. This element binds six proteins in vitro. We now report a mutational analysis of the HS4 HS-forming element (HSFE). This analysis indicates that binding sites for the hematopoietic transcription factors NF-E2 and GATA-1 are required for the formation of the characteristic chromatin structure of the HS following stable transfection into murine erythroleukemia cells. Similarly arranged NF-E2 and GATA binding sites are present in the other HSs of the human LCR, as well as in the homologous mouse and goat sequences and the chicken beta-globin enhancer. A combination of DNase I and micrococcal nuclease sensitivity assays indicates that the characteristic erythroid-specific hypersensitivity of HS4 to DNase I is the result of tissue-specific alterations in both nucleosome positioning and tertiary DNA structure.
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PMID:NF-E2 and GATA binding motifs are required for the formation of DNase I hypersensitive site 4 of the human beta-globin locus control region. 782 82

The distribution of the alpha and beta-globin genes and histone variants was examined in micrococcal nuclease-generated chromatin fractions of three Friend murine erythroleukemia cell types differing in malignant potential and inducibility to erythroid differentiation. A preferential concentration of globin gene sequences, as compared to satellite DNA, was noted in a physiological salt-soluble, histone H1-depleted, mononucleosomal chromatin fraction (Sup 120) in all Friend cell types, even those in which the globin gene was not capable of transcriptional activation by chemical induction. The level of globin gene enrichment in the Sup 120 fraction was highest in the most malignant and inducible cell type. The chemical induction of erythroid differentiation in this cell line did not change the distribution of globin genes in the chromatin fractions. The Sup 120 chromatin fraction prepared from mouse brain nuclei was not enriched in globin genes. Besides the previously reported low H2A. 1/H2A.2 ratio [Blankstein and Levy: Nature 260:638-640, 1976], chromatin from the most tumorigenic cell type showed the lowest H2B.2 to H2B.1 ratio, highest levels of histone H4 acetylation, and the most pronounced change in relative amounts of two major electrophoretic bands of histone H1 variants as compared to the less malignant cell types. The histone variant content of the micrococcal nuclease-generated chromatin fractions from the three Friend cell types reflected the core histone variant differences for the respective intact nuclei. However, the electrophoretic separation of mononucleosomes by size revealed several classes with different H2A variant ratios. The results demonstrate the existence of structural differences in globin gene and histone variants in erythroleukemia cell chromatin associated with distinguishable phenotypes during malignant cell progression.
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PMID:Distribution of globin genes and histone variants in micrococcal nuclease-generated subfractions of chromatin from Friend erythroleukemia cells at different malignant states. 812 82

The relationship between chromatin structure and endonuclease sensitivity was investigated. The cells used in this study were a) human myelogenous leukemic cell lines (HL-60, ML-I, U-937, THP-I) (Group I), which produced internucleosomal DNA cleavage, and b) human T-cell leukemia (MOLT-4), erythroleukemia (K562), glioblastoma (T98G, U87MG) and glioma (KG-1-C) cell lines (Group II), which produced no internucleosomal DNA cleavage, upon treatment with various apoptosis-inducing agents. When the nuclei, isolated from these cells were digested with micrococcal nuclease, chromatin DNA was cleaved into oligonucleosomal units. Although sensitivity to micrococcal nuclease considerably differed from cell to cell, Group I cells were generally more sensitive to micrococcal nuclease digestion than Group II cells. Similar sensitivity to DNase I was observed in both groups of cells. Acid-urea polyacrylamide gel electrophoresis of histone fractions from control and apoptosing HL-60 cells (induced either by hydrogen peroxide or UV irradiation) revealed no significant change in the relative composition of five major histones, indicating the absence of selective degradation of histone HI, but rather the nonspecific degradation of many nuclear proteins. These data suggest a difference in a chromatin structure between Group I and II cells, which might result in the selective production of internucleosomal DNA cleavage only in Group I cells.
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PMID:Chromatin structure and endonuclease sensitivity in human leukemic cell lines. 870 41

The genome structure and expression of mdr genes were examined in multidrug-resistant sublines of two different murine (DBA/2J) Friend erythroleukemia cell lines, PC4 and C7D, derived by stepwise exposure to increasing concentrations of adriamycin beginning with 5 ng/ml. The PC4 cell lines selected in higher drug concentrations (80-1280 ng/ml) demonstrated amplification of all three mdr genes with preferential amplification of mdr3. Overexpression of the mdr2 and mdr3 genes accompanied their genomic amplification; however, expression of mdr1 was not seen despite amplification. In the C7D cell lines selected with higher drug concentrations (40-160 ng/ ml), amplification and overexpression of mdr1 and mdr2 without mdr3 was observed. Increased expression of mdr1 occurred prior to gene amplification. The distribution of mdr-specific genes in micrococcal nuclease-generated chromatin fractions differing in transcriptionally active sequences and proteins was different between the parent and drug-resistant sublines. An enrichment (two- to threefold) of mdr3 genes in the H1-depleted mononucleosome fraction enriched for actively transcribed genes (e.g., globin) was detected by Southern analysis of chromatin fractions in PC4-80 cells (selected in 80 ng/ml of adriamycin and overexpressing mdr3), compared to the parental cells. mdr3 enrichment was also detected using a new PCR-based method, which examined mdr3 genes and repetitive sequences. Of note, the H1-depleted chromatin fraction from PC4-20 showed enrichment of the mdr3 gene, although mdr3 expression was not detected in the cell line. These studies showed a different pattern of gene amplification and overexpression in genetically related erythroleukemia cell lines selected for resistance to the same chemotherapeutic agent. A change in chromatin organization of mdr genes preceded overexpression and amplification of the mdr3 gene.
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PMID:Differential changes in genome structure and expression of the mdr gene family in multidrug-resistant murine erythroleukemia cell lines. 926 89


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