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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)

Calf thymus chromatin, depleted in histone H1, was digested with micrococcal nuclease and fractionated by column chromatography. 140 base pair nucleosome core particles were isolated along with an unusual particle containing 2 histone octamers and 240 base pairs of DNA. Evidence is presented that the spacer DNA region is absent from these modified dinucleosomes, which appear as stable products of the digestion process. The physical properties of both particles are presented along with brief speculation on their possible origin and function.
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PMID:Isolation and characterization of a spacerless dinucleosome from H1-deleted chromatin. 60 Jul 91

It has been demonstrated by digestion studies with micrococcal nuclease that reconstitution of complexes from DNA and a mixture of the four small calf thymus histones H2A, H2B, H3, and H4 leads to subunits closely spaced in a 137 +/- 7-nucleotide-pair register. Subunits isolated from the reconstituted complex contain nearly equimolar amounts of the four histones and sediment at 11.6S. On DNase I digestion both the reconstituted complex and the separated subunits gave rise to series of single-stranded DNA fragments with a 10-nucleotide periodicity. This indicates that the reconstitution leads to subunits very similar to nucleosome cores. Nucleosome cores closely spaced in a 140-nucleotide-pair register were also obtained upon removal of histone H1 from chromatin by dissociation with 0.63 M NaCl and subsequent ultracentrifugation. In reconstitution experiments with all five histones (including histone H1) our procedure did not lead to tandemly arranged nucleosomes containing about 200 nucleotide pairs of DNA. In the presence of EDTA, DNase II cleaved calf thymus nuclei and chromatin at about 200-nucleotide-pair intervals whereas in the presence of Mg2+ cleavage at intervals of approximately half this size was observed. The change in the nature of the cleavage pattern, however, was no longer found after removal of histone H1 from chromatin. This indicates that H1 influences the accessibility of DNase II cleavage sites in chromatin. This finding is discussed with respect to the influence of histone H1 on chromatin superstructure.
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PMID:Closely spaced nucleosome cores in reconstituted histone.DNA complexes and histone-H1-depleted chromatin. 63 Nov 38

The solubilization of nucleosomes and histone H1 with increasing concentrations of NaCl has been investigated in rat liver nuclei that had been digested with micrococcal nuclease under conditions that did not substantially alter morphological properties with respect to differences in the extent of chromatin condensation. The pattern of nucleosome and H1 solubilization was gradual and noncoordinate and at least three different types of nucleosome packing interactions could be distinguished from the pattern. A class of nucleosomes containing 13--17% of the DNA and comprising the chromatin structures most available for micrococcal nuclease attack was eluted by 0.2 M NaCl. This fraction was solubilized with an acid-soluble protein of apparent molecular weight of 20,000 daltons and no histone H1. It differed from the nucleosomes released at higher NaCl concentrations in content of nonhistone chromosomal proteins. 40--60% of the nucleosomes were released by 0.3 M NaCl with 30% of the total nuclear histone H1 bound. The remaining nucleosomes and H1 were solublized by 0.4 M or 0.6 M NaCl. H1 was not nucleosome bound at these ionic strengths, and these fractions contained, respectively, 1.5 and 1.8 times more H1 per nucleosome than the population released by 0.3 M NaCl. These fractions contained the DNA least available for micrococcal nuclease attach. The strikingly different macromolecular composition, availability for nuclease digestion, and strength of the packing interactions of the nucleosomes released by 0.2 M NaCl suggest that this population is involved in a special function.
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PMID:Fractionation of nucleosomes by salt elution from micrococcal nuclease-digested nuclei. 70 81

Chromatin subunits ("nucleosomes") isolated from a mild staphylococcal nuclease digest of chromatin by a sucrose gradient centrifugation have been studied. We found that such preparation contains nucleosomes of the two discrete types which can be separated from each other by a low-ionic-strength polyacrylamide gel electrophoresis. Nucleosome of the first type contains all five histones and a DNA fragment 170--180 base pairs long, whereas nucleosome of the second type lacks histone H1 and its DNA fragment is approximately 140 base pairs long. Purified dimer of the nucleosome (dinucleosome) can be fractionated by gel electrophoresis into three discrete bands which correspond to dinucleosomes, containing two, one and no molecules of H1 histone. Similar heterogeneity with respect to the content of histone H1 probably exists in the case of larger oligonucleosomes. These and related findings strongly suggest that the H1 molecule is bound to a short (30--40 base pairs) terminal stretch of the nucleosomal DNA segment which can be removed by nuclease (possibly in the form of H1--DNA complex) without any significant disturbance of the main structural features of the nucleosome.
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PMID:[Structure of chromosomal deoxyribonucleoproteins. IX. Heterogeneity of chromatin subunits in vitro and location of histone H1]. 75 77

Oligomers of chromatin subunits (oligonucleosomes) were prepared by a mild digestion of chromatin with staphylococcal nuclease followed by a purification of a high molecular weight material (hexanucleosomes and larger DNP particles) by gel chromatography. The main finding is that a mild removal of histone H1 from the oligonucleosome preparation by treatment with tRNA in the absence of any significant hydrodynamic shearing leads to the formation of free DNA molecules which constitute 5-6% of the total oligonucleosomal DNA. The size of nucleosome-free DNA stretches in H1-depleted hydrodynamically sheared chromatin is about 6000 base pairs and their content is apparently 10-12% of the total DNA. These and related findings are discussed in terms of the previously proposed "asymmetric hairpin" model of DNA packing in chromatin [1-4]. Different kinds of the asymmetric hairpin are considered and ambiguities in interpretations of experimental data are pointed out.
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PMID:Free DNA stretches in histone H1-depleted chromatin and their possible relation to chromomere structure. 100 4

The structure of chicken erythrocyte and chicken liver chromatin has been studied by enzymatic digestion with micrococcal nuclease and DNAase I. Comparison of the fragments produced by brief digestion with micrococcal nuclease indicates that chicken erythrocyte chromatin has a longer nucleosome repeat than chicken liver chromatin, 212 base pairs as opposed to 200 base pairs (bp). More extensive digestion with micrococcal nuclease demonstrates that both tissues have 140 bp mucleosome cores. The difference in the length of the nucleosome repeat must therefore result from a difference in the length of the DNA linker between cores. Chicken erythrocyte chromatin is known to contain a tissue-specific, H1-like histone, H5, and to be genetically dormant. A model is presented to explain how changes in histone H1 could cause changes in the nucleosome repeat length and thereby alter the genetic activity of chromatin.
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PMID:A comparison of the structure of chicken erythrocyte and chicken liver chromatin. 100 80

Chromatin prepared by brief digestion of nuclei with micrococcal nuclease, and extracted in 0.2 mM EDTA, appears in the electron microscope as filaments of about 100 A diameter which coil loosely. In 0.2 mM Mg++ these "nucleofilaments" condense into a supercoil or solenoidal structure of pitch about 110 A corresponding to the diameter of a nucleofilament. It is proposed that the x-ray reflections at orders of 110 A observed in chromatin originate in the spacing between turns of the solenoid rather than that between nucleosomes along the nucleofilament. The solenoidal structure appears to need histone H1 for its stabilization. Under certain conditions, isolated nucleosomes can also aggregate into a similar structure. The solenoidal structure can be correlated with the "thread" of diameter about 300 A observed by other workers in nuclei.
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PMID:Solenoidal model for superstructure in chromatin. 106 61

Earlier findings /1-10/ bearing on a subunit organization of chromatin were confirmed and in some points detailed. Besides this, a large-scale isolation of chromatin subunits; their protein composition, electron microscopic appearance and CsCl banding pattern are described. Although the purified chromatin subunit contains all five histones, the relative content of histone H1 i in it is two times lower than that in the original chromatin. tit is shown that a mild digestion of chromatin with staphylococcal nuclease produced not only separate chromatin subunits and their "oligomers' but also deoxyribonucleoprotein particles which sediment more slowly than subunits. It appears that these particles and subunits are produced from different initial structures in the chromatin. Finally, a crystallization of the purified chromatin subunit as a cetyltrimethyl ammonium salt is described.
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PMID:Studies on chromatin. II. Isolation and characterization of chromatin subunits. 117 23

Chromatin subunits ("nucleosomes") which were purified by sucrose gradient centrifugation of a staphylococcal nuclease digest of chromatin have been studied. We found that such a preparation contains nucleosomes of two discrete types which can be separated from each other by polyacrylamide gel electrophoresis. Nucleosome of the first type contains all five histones and a DNA segment of approximately 200 base pairs long, whereas nucleosome of the second type lacks histone H1 and its DNA segment is approximately 170 base pairs long, i.e., about 30 base pairs shorter than the DNA segment of the nucleosome of the first type. Purified dimer of the nucleosome also can be fractionated by gel electrophoresis into three discrete bands which correspond to dinucleosomes containing two molecules of histone H1, one and no H1. These and related findings strongly suggest that the H1 molecule is bound to a short (approximately 30 base pairs) terminal stretch of the nucleosomal DNA segment which can be removed by nuclease (possibly in the form of H1-DNA complex) without any significant disturbance of main structural features of the nucleosome.
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PMID:Heterogeneity of chromatin subunits in vitro and location of histone H1. 125 57

Recent evidence indicates that chromatin accessibility to transcription factors is of regulatory significance. The polyanion heparin is known to increase chromatin accessibility to DNAase I and to stimulate both RNA and DNA synthesis. In the present study, chromatin structure and its modification by polyanions were examined by using trypsin and micrococcal nuclease as probes. Both heparin and poly(glutamic acid) were found to be equivalent to trypsin digestion of histones in their ability to increase nuclease accessibility in chromatin. However, no increase in nuclease accessibility was observed when trypsin-digested chromatin was further treated with heparin, indicating that polyanions and trypsin are not additive in their effects on chromatin accessibility. Moreover, sucrose-gradient analysis demonstrated that heparin binds tightly to intact nucleosomes but not to trypsin-digested nucleosomes. These data suggest that polyanions interact predominantly with the trypsin-sensitive lysine and arginine residues in histone H1 and the N-terminal segments of the core histones. The possible relevance of these results to the chromatin structure of actively transcribed regions is discussed.
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PMID:Heparin increases chromatin accessibility by binding the trypsin-sensitive basic residues in histones. 128 84


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