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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)

In eukaryotic cells, transcriptionally active chromatin and inactive chromatin exist in dissimilar configurations which correlate with their functional states. The present study asks whether the differences in structure and function of active and inactive chromatin are also reflected in the process of replication. We have used mild micrococcal nuclease digestion [Bloom, K.S., & Anderson, J.N. (1978) Cell (Cambridge, Mass.) 15, 141-150] to release selectively an active chromatin fraction, S1, from MSB cell nuclei. The S1 fraction is greater than 6-fold enriched in sequences complementary to polyadenylated RNA and thus consists of virtually pure active chromatin. As isolated, the S1 chromatin comprises mononucleosomes which contain approximately 160 base pairs of DNA bound by core histones but which are enriched in non-histones and free of histone H1. Chemical cross-linking of S1 chromatin yields octamers containing the normal stoichiometry of core histones. When MSB cells are pulse labeled with isotopically dense amino acids and the recovered S1 chromatin is isolated and cross-linked, the labeled histone octamers are found in a single hybrid density octamer band on isopycnic gradients. These results indicate that, in contrast to the conservative assembly of transcriptionally inactive nucleosomes, the deposition of histones during the replication of active chromatin follows a nonrandom, semiconservative pathway.
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PMID:Assembly of active chromatin. 370 32

Scrapie affected brains exhibit a number of pathological features in common with the human neurodegenerative condition, Alzheimer's disease. The present report describes studies on chromatin structure seen in these two disease processes. Chromatin associated proteins influence transcriptional activity of DNA through an effect upon chromatin structure. We examined chromatin structure by: measuring the capacity of the enzyme micrococcal nuclease to release mono- and dinucleosomes from isolated nuclei and measuring DNA-histone interactions by examining the effect of ambient tonicity upon the release of chromatin proteins. In two strains of mice infected with two strains of scrapie agent there was reduced accessibility to micrococcal nuclease and an increased content on dinucleosomes of the histone H1 and H1(0) types. These changes precede clinical signs of scrapie and resemble those found in the human conditions of Alzheimer's and Pick's disease. Scrapie mouse brain differs from Alzheimer brain in that scrapie does not alter histone-DNA interactions as monitored by ionically induced histone release from chromatin. Despite similarities, the scrapie agent appears to operate upon different molecular mechanisms than those found in Alzheimer's disease.
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PMID:Chromatin structure in scrapie and Alzheimer's disease. 379 Oct 58

Digestion of sea urchin sperm nuclei with micrococcal nuclease yields nucleosomal monomer fragments of 151 and 164 base pairs. Prior trypsin treatment of the sperm chromatin does not alter the size of these monomer DNA fragments despite the fact that the H1 histone is reduced to a limit globular peptide of about 83 residues. Heterologous reconstitution experiments show that this peptide is capable of protecting an extra 22 base pairs beyond the core particle in a chromatosome. Nuclease digestion of reconstitutes from DNA and sperm core histones yields a core monomer of about 141 base pairs. It is concluded that this sperm chromatin contains a chromatosome of 164 bp essentially similar to that observed in the more usual chromatins. Edman degradation of the H1 limit peptide shows its sequence to be closely analogous to the corresponding peptide of calf H1 and chicken H5. Circular dichroism studies of histone H1 from the sperm of three sea urchin species demonstrate the presence of trypsin-sensitive helical regions outside the globular domain that are absent in calf H1 and chicken H5.
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PMID:The chromatin of sea urchin sperm. 380 86

Binding of the glucocorticoid receptor complex to nucleosomes has been studied using the mouse P1798 lymphosarcoma. Cells were incubated with [3H]triamcinolone acetonide (TA), and nuclei prepared and digested with 3 different concentrations of micrococcal nuclease. After fractionation with EDTA and NaCl, it was observed that [3H]TA bound with similar specific radioactivity to mononucleosomes containing both core and linker DNA, of 183 +/- 5, and 168 +/- 4 base pair lengths, respectively, as well as to core size DNA, of 148 +/- 3 base pair length, suggesting that the glucocorticoid receptor bound to the core portion of the nucleosome. Steroid binding was found to be associated with regions of the nucleosome that were depleted in histone H1 and enriched in high mobility group (HMG) proteins 1 and 2; only negligible binding was noted in nucleosomes enriched in histone H1 and depleted in HMG proteins. In addition to binding to core nucleosomes, the glucocorticoid receptor complex was also shown to bind to a fraction sedimenting at 5-6 S on sucrose gradients characterized by subnucleosome and mononucleosome size DNA, as well as by core histones. While binding of the steroid receptor complex to linker regions of the nucleosome cannot be ruled out, this data would appear to present the first concrete evidence that glucocorticoid binding, at least in the P1798 lymphosarcoma, is to core nucleosomes. Some caution in interpretation of the results is indicated, however, on 2 points: (1) receptor redistribution during nuclease digestion cannot be ruled out; (2) only the binding of a small proportion of the steroid receptor complex may be physiologically relevant.
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PMID:Binding of the glucocorticoid receptor complex to the nucleosomal core in the P1798 mouse lymphosarcoma. 392 86

Light treatment of nuclei of Physarum polycephalum microplasmodia with DNase I, at low MgCl2 concentration (less than or equal to 3% DNA acid solubility, 0.1 mM MgCl2) selectively solubilizes a defined fraction of chromatin, in the form of a macromolecular complex. This fraction (up to 15% of the total chromatin) contains a full complement of the core histones and a reduced amount of histone H1, and is enriched in the high-mobility-group type of proteins. It is preferentially associated with nascent RNA and RNA polymerase B actively engaged in transcription. Digestion of DNAase-I-solubilized chromatin by micrococcal nuclease releases a size-heterogeneous population of cleavage products, indicative of lack of a typical nucleosomal packaging. It is concluded that the procedure used allows the isolation of structurally and functionally distinct regions of Physarum chromatin.
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PMID:Lack of nucleosomal structure in a DNase-I-solubilized transcriptionally active chromatin fraction of Physarum polycephalum. 397 88

Micrococcal nuclease digestion and light scattering are used to compare native chromatins with various histone H1[0] contents. The experimental data show that the higher the H1[0] content, the greater the ability to form compact structures with increasing ionic strength, and the lower the DNA accessibility to micrococcal nuclease. On the contrary, reconstituted samples from H1-depleted chromatin and pure individual H1 fractions behave in such a way that samples reconstituted with pure H1 degree give rise to a looser structure, more accessible to nuclease than samples reconstituted with H1-1. This contradiction suggests that the effect of H1o on chromatin structure must originate from the interaction of this histone with other components in native chromatin among which other histone H1 subfractions are good candidates.
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PMID:The involvement of histone H1[0] in chromatin structure. 400 Sep 66

We have investigated the micrococcal nuclease digestion of chromatin from the spermatozoa of the sea cucumber Holothuria tubulosa. This chromatin contains minor protein variants related to histone H1 with a high proportion of basic amino acids. One of these variants, protein phi 0, represents about 4% of the total histones. It is 78 amino acids long and its amino acid composition and sequence are related to the very basic C-terminal region of histone H1. The presence of these proteins induces an unusual digestion pattern. Oligonucleosomal particles which are soluble at 150 mM NaCl are depleted of protein phi 0 and they are also defective in histone H1. A low percentage of the insoluble material can be solubilized at lower NaCl concentrations (50 mM). These oligonucleosomal particles show a very peculiar protein content, since at early digestion times, they contain histone H1 and protein phi 0 exclusively. We conclude that these particles arise from a cooperative displacement of core histones by protein phi 0 and histone H1. These results show that minor changes in histone H1 complement can result in the formation of artifactual particles upon microccocal nuclease digestion. These observations may be of interest in other systems which contain H1 variants.
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PMID:Anomalous nuclease digestion of Holothuria sperm chromatin containing histone H1 variants. 403 61

Chromatin fractions differing in their transcriptional activity were isolated by selective micrococcal nuclease digestion of nuclei from sea urchin embryos (Strongylocentrotus droebachiensis) at the gastrula and pluteus stage. The electrophoretic analysis of the chromatin proteins at the gastrula stage showed that a soluble, transcriptionally active fraction of chromatin was enriched with early variants of histones H1 and H2A. The early and late variants of histone H2A at the pluteus stage were distributed randomly between chromatin fractions. However, the content of both variants of histone H1 was essentially decreased in the soluble transcriptionally active fraction of chromatin.
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PMID:Distribution of histone variants in the sea urchin chromatin fractions obtained by selective micrococcal nuclease digestion. 406 5

The technique of freeze-drying was applied to examine the submicroscopic organisation of metaphase chromosomes from Chinese hamster after removal of bivalent cations with EDTA and removal of histone HI with 0,6 M NaCl. Treated chromosomes increased in size, and nucleosomal filaments appeared at the periphery of the chromosomes. Removal of bivalent cations is accompanied with the appearance of regularly organized structures of the "beads-on-a-string" type. The regular organization of the fibers is damaged as soon as histone H1 is removed. After decondensation in a 0.6 M NaCl solution the metaphase chromosomes were treated with staphylococcal nuclease in situ on EM grids nd the residual structures analysed using electron microscopy. Nucleohistone fibers wer visible at the periphery of the chromosomes at the beginning of digestion. After complete elimination of the nucleohistone fibers in the course of digestion the remaining proteinaceous material was represented by aggregates of irregular shape and of varying size. These were either concentrated along the central axis of the chromatids or, at the final step of digestion, scattered evenly over the entire area that had been occupied by the chromosome. Presumably, in the chromosome prior to digestion, the material did not form an integral protein structure similar to a scaffold in dehistonised and spread chromosomes. An alternative interpretation for the fragmentation of protein material in the chromosome considers possible degradation of the protein scaffold in the course of digestion.
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PMID:The structure of partly decondensed metaphase chromosomes. 618 61

Chromatin of immature testes and sperma of grass carp and carp was hydrolyzed by micrococcal nuclease and DNA I. The hydrolysis kinetics was studied. Chromatin of sperm maintains the nucleosomal repeat typical to somatic cells and is more resistant to the nuclease effect than chromatin of testes. Histones H1 and H2B of grass carp differ from the respective histones of the calf thymus. The core histones of sperm testes and liver chromatin in grass carp and carp have similar electrophoretic mobility. However the amount of slowly moving subfraction of histone H1 increases in the course of spermatogenesis. The amino acid composition of histone H1 from the carp sperm is characterized by a high lysine (34.6%) and low glycine (4.5%) content. A histone H1 molecule contains one tyrosine. The lysine/arginine ratio is 21.6 which is considerably higher than in H1-like histones of sperma in other species (for instance of Echinodermata).
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PMID:[Accumulation of one of the histone H1 subfractions and increase in chromatin resistance to the nuclease effect in the course of carp and grass carp spermatogenesis]. 622 17


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