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:3.1.31.1 (micrococcal nuclease)
2,818 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A novel nucleohistone particle is generated in high yield when a complex of DNA with the four core histones formed under conditions that are close to physiological (0.15 M NaCl, pH 8) is treated with micrococcal nuclease. The particle was found to contain 102 base pairs of DNA in association with six molecules of histones in the ratio 2H2A:2H2B:1H3:1H4 after relatively brief nuclease treatment. Prolonged nuclease digestion resulted in a reduction in the DNA length to a sharply defined 92-base pair fragment that was resistant to further degradation. Apparently normal nucleosome core particles containing two molecules each of the four core histones in association with 145 base pairs of DNA and a particle containing one molecule each of histones H2A and H2B in association with approximately 40 base pairs of DNA were also generated during nuclease treatment of the histone-DNA complexes formed under physiological ionic strength conditions. Kinetic studies have shown that the hexamer particle is not a subnucleosomal fragment produced by the degradation of nucleosome core particles. Furthermore, the hexamer particle was not found among the products of nuclease digestion when histones and DNA were previously assembled in 0.6 M NaCl. The high sedimentation coefficient of the hexameric complex (8 S) suggests that the DNA component of the particle has a folded conformation.
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PMID:The assembly of an H2A2,H2B2,H3,H4 hexamer onto DNA under conditions of physiological ionic strength. 663 Feb 31

The composition and structure of three discrete nucleohistone particles produced by micrococcal nuclease digestion of the complex formed when the four core histones are mixed directly with DNA under conditions that are close to physiological have been reported in accompanying articles (Ellison, M. J., and Pulleyblank, D. E. (1983) J. Biol. Chem. 258, 13307-13313; 13314-13320). These include a peak containing a compact hexameric complex composed of one pair of (H3,H4) and two pairs of (H2A,H2B) (P2) and a peak containing complexes with the composition and sedimentation properties of nucleosome cores (P3). We have examined the pathways of assembly of P2 and P3 by determining the effect of order of histone addition on the yields of these species. The assembly of P2 is initiated by the binding of an (H2A,H2B) pair to the DNA which then directs the placement of an (H3,H4) pair. The incorporation of the final (H2A,H2B) pair to complete the particle is probably cooperative. The assembly of P3 is less dependent than the assembly of P2 upon the order in which the histone pairs are added to the DNA. More than one pathway has been implicated in the formation of these particles. P3 contains a component which has many but not all of the properties of nucleosome cores assembled at elevated ionic strength. Alternative pathways of assembly of histone pairs onto DNA are discussed which could lead to the formation of the discrete histone DNA structures that have been isolated here. A model is proposed in which the nucleosome unfolds and refolds into an alternative configuration.
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PMID:Pathways of assembly of nucleohistone complexes formed in vitro under physiological conditions. Implications for the structure of the nucleosome. 663 Feb 33

An activity which facilitates assembly of nucleosome-like structures in vitro at physiological ionic strength was detected both in human HeLa S3 cells and mouse FM3A cells. The assembly protein was purified from FM3A cells by fractionation with ammonium sulfate, DEAE-cellulose, phosphocellulose, Sephadex G-150 column chromatography, and sucrose gradient centrifugation. In the sucrose gradient, the activity was detected at 5S and the active fraction contained three peptides of 59,000, 65,000, and 102,000 daltons. When core histones were mixed with these peptides, the 59,000 peptide sedimented at the 6S and 10S positions, where the histones co-sedimented. The 6S fraction contained H2A, H2B, and A24 proteins, and the 10S fraction contained four kinds of core histones in equal amounts. Nucleosomes were formed by mixing DNA with the 10S fraction, but were not formed with the 6S fraction. The nucleosome structure assembled was assessed using the sensitivity to micrococcal nuclease.
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PMID:A protein which facilitates assembly of nucleosome-like structures in vitro in mammalian cells. 664 19

We have studied the functional properties of iodinated histones. Isolated, denatured histones were iodinated at trace levels and then renatured together with carrier histones and high molecular weight DNA to form nucleohistone. Nucleosomes were prepared from the reconstitute using micrococcal nuclease, and the relative representations of the individual iodinated tyrosines of the histones in the reconstituted nucleosomes were determined. Our principal findings are 1) that denatured histones can be iodinated at any tyrosine without interfering in subsequent nucleosome reconstitution and 2) that the resulting reconstituted nucleosomes nevertheless possess histone cores of altered stability, being either more or less stable depending on the particular tyrosine which is iodinated. We show that tyrosines 37, 40, and 42 of H2B are protected from iodination in intact core particles, as expected since these tyrosines lie within the H2B-H2A binding site. Yet iodination of these tyrosines in denatured H2B does not interfere with nucleosome assembly. However, the histone cores isolated from these reconstituted nucleosomes are of diminished stability as assayed by Sephadex column chromatography in 2 M salt. In contrast, iodination of tyrosines 83 and 121 of H2B, as well as iodination of the tyrosines of H2A, increases the stability of the histone octamer core. Iodination of H4 tyrosine 72 is without effect on histone octamer stability. Tyrosine iodination constitutes a profound amino acid alteration in the context of the absolute evolutionary conservation of most histone tyrosines. For example, all H2Bs sequenced to date, from fungi to mammals, possess tyrosines at positions 37, 40, and 42. Our results suggest that the immutability of these tyrosines reflects some sophisticated function of the nucleosome histone core beyond the assembly and mere maintenance of a compact structure.
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PMID:Role of histone tyrosines in nucleosome formation and histone-histone interaction. 670 50

Nuclei from butyrate-treated or control HeLa cells were separated into micrococcal nuclease sensitive and resistant chromatin. Those regions most sensitive to the nuclease, amounting to some 10% of the chromatin, consisted mainly of mononucleosomes with equimolar amounts of the inner histones H2A, H2B, H3, and H4, very little H1, and equimolar amounts of the two small high-mobility group (HMG) proteins, HMG-14 and -17. Both in butyrate-treated and in control cells, these nuclease sensitive monomers were some 5--7-fold enriched in DNA sequences which are transcribed into cytoplasmic polyadenylated RNA, while resistant monomers are depleted in the same sequences. Electrophoretic analyses of the transcriptionally active mononucleosomes revealed heterogeneity. Several subcomponents were resolved when monomers of butyrate-treated or control cells were electrophoresed at low ionic strength. Active monomer subcomponents differ in their molar content of HMG-14 and -17, in their content of H1 and A24, and in the length of their DNA. Some minor differences between nucleosomes of butyrate-treated and control cells were observed.
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PMID:Structure of transcriptionally active and inactive nucleosomes from butyrate-treated and control HeLa cells. 689 35

A histone-like protein (H) from Escherichia coli has been purified to more than 98% homogeneity by using its capacity to inhibit DNA functions. H protein behaves as a dimer of 28,000-dalton subunits. The histone H2A-like properties of H protein are: (i) binding to DNA at a stoichiometry of 1 H protein dimer per 75 bases; (ii) abundance of about 30,000 molecules per cell, sufficient to bind about 20% of the chromosome; (iii) limiting digestion of double-stranded DNA by micrococcal nuclease; (iv) reannealing of complementary single-stranded DNA; (v) amino acid composition resembling that of eukaryotic histone H2A; (vi) neutralization of H protein by antibody specific for H2A; (vii) heat stability; and (viii) acid solubility. The capacity of H protein to bind DNA prevents its template or substrate functions n several reactions in vitro: DNA synthesis by several polymerases; transcription by RNA polymerase; DNA topoisomerase activity; and DNA-dependent ATP hydrolysis by rep protein, dnaB protein, or protein n'. Together with other histone-like proteins of E. coli, H protein may organize the E. coli chromosome into nucleosomes, such as in eukaryotic chromatin.
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PMID:Novel histone H2A-like protein of escherichia coli. 700 71

We have described earlier a chromatin-bound protease with unique specificity for histone H2A [Eickbush, T. H., Watson, D. K., & Moudrianakis, E. N. (1976) Cell (Cambridge, Mass.) 9, 785--792]. In the present study, we explore the nature of interactions that form and stabilize the enzyme-chromatin system by using the activity of the protease to monitor its binding to DNA and DNA-histone complexes. During salt extraction of chromatin, the protease is released at an ionic strength between that required for the extraction of the slightly lysine-rich histones (H2A and H2B) and the arginine-rich histones (H3 and H4). The reassociation of this nonhistone protein to DNA has an absolute requirement for the H3--H4 tetramer and is only enhanced by the H2A--H2B dimer in the presence of the tetramer. We believe that the binding of the enzyme onto DNA requires some histone-elicited compaction of the helix. We have also examined the distribution of this enzyme within the chromatin fiber by isolating pools of monomer nucleosomes from micrococcal nuclease digests of 0.6 M NaCl extracted chromatin and from reconstituted DNA-protein complexes. The H2A-protease is found with these monomer nucleosome pools, and no activity can be detected in the low molecular weight products released during the digestion. Thus, by virtue of its extraction characteristics from chromatin and its association with isolated nucleosomes, this nonhistone protein exhibits properties hitherto assigned only to the inner histones.
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PMID:Histone-dependent reconstitution and nucleosomal localization of a nonhistone chromosomal protein: the H2A-specific protease. 704 60

Mononucleosomes isolated from micrococcal nuclease digests of stationary phase chromatin of the yeast Saccharomyces cerevisiae were compared both compositionally and physiochemically with those from chicken and bovine calf. It was found that while yeast mononucleosomes are similar in composition, their thermal denaturation profiles and circular dichroism spectra indicate a less constrained structure. Furthermore, yeast nucleosomes were discovered to be labile in solutions of low ionic strength and could not be reconstituted by methods applicable to calf and chicken nucleosomes. On the basis of the reconstitution of a hybrid nucleosome containing calf histones H2A, H2B, and H3 and yeast histone H4, it was concluded that variations in the yeast H4 sequence are unlikely to be responsible for the apparent decrease in the stability of yeast nucleosomes. Examinations of histone-histone interactions in free solution revealed a change in the H3-H4 interaction and together with the previously published results of other researchers it was inferred that changes in the H3 sequence might be responsible for this structural variation.
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PMID:Structural studies on yeast nucleosomes. 704 1

During spermatogenesis in the winter flounder, the average repeat length of nucleosomal DNA in the testis increases from 195 +/- 2 base pairs in prespermatid nuclei to 222 +/- 3 base pairs in sperm. This increase in repeat length apparently occurs in the linker region since there is no change in the pattern of DNA fragments produced during micrococcal nuclease digestion of the nucleosome core. The timing of the increase coincides with the loss of phosphate from the high molecular weight basic nuclear proteins and histones H2A and H4. When prespermatid nuclei are digested with micrococcal nuclease to the point where 10% of the DNA is acid-soluble, mononucleosomes and higher oligomers are readily released. However, when sperm chromatin is digested to the same extent, these products are no longer soluble and only traces of H1 and small DNA fragments are released. This situation is not changed in sperm chromatin that has been depleted of H1 by extraction with 0.4 M NaCl. However, if nuclease-treated sperm chromatin is lightly digested with trypsin, mono- and oligonucleosomes are released. At this level of proteolysis, the high molecular weight basic nuclear proteins are completely broken down, but the core histones are largely intact. These data are consistent with a model in which the unphosphorylated high molecular weight basic nuclear proteins function in cross-linking nucleosomes together within the sperm nucleus.
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PMID:Chromatin reorganization during spermatogenesis in the winter flounder. 710 49

Some of the properties of chromatographically purified satellite chromatin are compared with those of unfractionated, control chromatin. Nucleosomes were present in the purified satellite chromatin as verified by digestion with micrococcal nuclease and DNase I and by electron microscopy. Average nucleosome DNA repeat lengths of 186 +/- 7 and 193 +/- 5 base pairs were obtained through micrococcal nuclease digestion of the purified satellite chromatin and control chromatin, respectively; nucleosome spacer lengths were equally heterogeneous for the two chromatin samples. The distribution of Eco RI-produced chromatin fragments of different size in the satellite chromatin was the same as that calculated assuming random cleavage at each Eco RI site, consistent with the notion that nucleosomes do not have specific locations on the 1.715 g ml-1 satellite DNA. The purified satellite chromatin contained little non-histone protein, but did contain all five histones and all detectable histone sequence variants. Amounts of the core histones were identical in the satellite chromatin and the control chromatin, but the amount of histone H1 was 30% less in the satellite chromatin than in the control. Although the molar ratios for the major sequence variants of both histones H3 and H2A differed between kidney and thymus, the ratios were the same for satellite and control chromatin isolated from a single tissue.
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PMID:Chromatin fragments containing bovine 1.715 g ml-1 satellite DNA. Nucleosome structure and protein composition. 711 10


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