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At least 19 recordsLinked to original sources
PubMed1992

Deoxyribonucleoprotein structure and radiation injury: cellular radiosensitivity is determined by LET infinity -dependent DNA damage in hydrated deoxyribonucleoproteins and the extent of its repair.

For decades, theories of cellular radiosensitivity relied upon the initial patterns of energy deposition to explain radiation lethality. Such theories are unsound: cellular (DNA) repair also underlies cellular radiosensitivity. For the charged particles encountered in deep space, both the types of DNA damage caused in cellular deoxyribonucleoproteins and the efficacies of their repair are dependent on linear energy transfer (LET infinity), and repair efficiency is also influenced by cell and tissue type, i.e., the actual recovery processes involved. Therefore, quality factors derived from radiation quality alone are inadequate parameters for assessing the radiation risks of space flight. Until recently, OH radicals formed in bulk nuclear water were believed to be the major causes of DNA damage that results in cell death, especially for sparsely ionizing radiations. That hypothesis has now been challenged, if not refuted. Lethal genomic DNA damage is determined mainly by energy deposition in deoxyribonucleoproteins, and their hydration shells, and charge (energy) transfer processes within those structures.

Animals↗
PubMed1975

Studies on deoxyribonucleoproteins. IX. Subfractions of deoxyribonucleoproteins from rat and mouse liver.

By carrier-free continuous electrophoresis, deoxyribonucleoprotein from rat and mouse liver could be separated into two subfractions. The more anodic fraction (DNP I), comprising 5 - 8 per cent of the total, contains fewer proteins (two types of histones only). [3H]Cyclophosphamide caused in vivo a 2.5 times higher alkylation of the DNA in in DNP I than of the DNA in DNP II. These and additional results led to the suggestion of a structural model with DNP I as a spacer in the deoxyribonucleoprotein fiber.

Animals↗
PubMedDate not supplied

[Structure of chromosomal deoxyribonucleoproteins. XI. Organization of deoxyribonucleoprotein complex in bacterial cells].

Isolation of bacterial chromosomes under "mild" conditions enable us to purify a bacterial deoxyribonucleoprotein (DNP). This DNP is enriched in small basic proteins which are complexed with DNA throughout all the purification steps. The basic proteins are shown to be similar to some heat-resistant proteins of cellular extract and can interact with DNA in vitro. Extensive nuclease digestion of purified DNP of E. coli produced the smallest DNA fragments of 100--120 base pairs in length. The proteins of the DNP and the possible mode of arrangement of basic proteins along the DNA are discussed.

Base Composition↗
PubMed1966

Structure and properties of rat-thymus deoxyribonucleoprotein. A comparison of the electric birefringence and other properties of deoxyribonucleoprotein prepared by various methods.

1. A comparison has been made of the properties of dNP (deoxyribonucleoprotein) prepared in various ways from rat thymus. The variables studied were: (a) extent of homogenization; (b) concentration of various metal ions; (c) concentration of EDTA; (d) extent of dialysis; (e) concentration of dNP. The chief method used for studying the dNP was that of electric birefringence; this gives information about the optical and electrical properties of molecules oriented in an electric field and about their length. 2. The extent of homogenization during the preparation affects the birefringence properties only slightly and the solubility properties of the constituent DNA not at all. However, the protein content of the dNP decreases after repeated homogenization. 3. In the presence of added Ca(2+), Mg(2+) or Na(+) an insoluble product is obtained. 4. The presence of added EDTA affects the birefringence properties only slightly. 5. In the final stage of preparation, both very limited dialysis and extensive dialysis (in terms of volume ratio) cause partial insolubility of the final product. 6. dNP prepared at low concentrations resembles in some respects dNP prepared at higher concentrations and then subjected to limited enzyme action but it is not degraded (as by extensive enzyme action); ultracentrifuge studies of the constituent DNA confirm that no degradation of the DNA has occurred. 7. It is concluded that dNP prepared at low concentrations or by extensive dialysis is denatured and that preparation of ;native' material is favoured by maintenance of a high dNP concentration and by fairly limited dialysis.

Animals↗
PubMed1981

Changes of deoxyribonucleoprotein in the spleen, thymus and liver of rats exposed to weightlessness and artificial gravity aboard the Cosmos biosatellites.

Changes of deoxyribonucleoprotein in the spleen, thymus and liver of rats exposed to weightlessness or artificial gravity on board biosatellites Cosmos 782 and Cosmos 936 after 20 days of flight were investigated. The level of polydeoxyribonucleotides in the spleen and thymus of rats exposed during the flight to weightlessness increased 4-11 hours after landing, suggesting breakdown of a part of the deoxyribonucleoprotein present. The use of artificial gravity prevented this breakdown in the thymus but not in the spleen. The breakdown was accompanied in the majority of cases by a decrease in the deoxyribonucleoprotein content. We believe the breakdown of deoxyribonucleoprotein is due to a nonspecific stress reaction to the change from the weightless state to that of terrestrial gravity during landing. The polydeoxyribonucleotide level and amount of deoxyribonucleoprotein in the majority of cases returned to normal values during the 25 days of readaptation. No substantial change of deoxyribonucleoprotein was found in the liver. The different findings in the three organs are due to the fact that breakdown of deoxyribonucleoprotein takes place in sensitive cells underlying pycnosis. These cells are found in the spleen and thymus, but not in the liver.

Animals↗
PubMed1967

Structure and properties of rat thymus deoxyribonucleoprotein. Solubility properties and effects of precipitation.

1. Deoxyribonucleoprotein was prepared from rat thymus and was studied chiefly by the method of electric birefringence. The birefringence depends on the electrical and optical properties of the molecules and on their volume; the decay time of birefringence (after the removal of the electric field) depends on molecular length. 2. A comparison was made of the properties of deoxyribonucleoprotein redissolved after precipitation in 0.15m-sodium chloride with those of the original material, the main object being to find if structural changes have occurred in the former. As a preliminary, the dependence of the solubility of the deoxyribonucleoprotein on the concentration of added salt was investigated, and the birefringence properties were also studied after the addition of sodium chloride at low concentrations, after the alteration of pH and after dialysis. 3. It was found that precipitation of deoxyribonucleoprotein occurs in two fractions, beginning at about 0.4mm-sodium chloride. The solubility is minimal at about 0.15m-sodium chloride. 4. The electric birefringence and decay time of the deoxyribonucleoprotein decrease with increasing concentration of added sodium chloride, and the birefringence also decreases after dialysis. Prolonged dialysis leads to precipitation. 5. The properties of deoxyribonucleoprotein redissolved after precipitation with 0.15m-sodium chloride differ considerably from those of the original deoxyribonucleoprotein. This is attributed to some type of disorganization process occurring during precipitation. It is concluded that the organization of the original structure is very specific.

Animals↗
PubMed1971

Studies on the accessibility of deoxyribonucleic acid in deoxyribonucleoprotein to cationic molecules.

The binding of deoxyribonucleoprotein to Toluidine Blue, to cetylpyridinium chloride and to polylysine of various molecular weights was studied to determine the percentage of free DNA phosphate groups in deoxyribonucleoprotein. Binding was measured by addition of these reagents to deoxyribonucleoprotein at a range of concentrations such that complete precipitation of the deoxyribonucleoprotein occurred. With Toluidine Blue the binding corresponded to about 48% of the DNA phosphates in deoxyribonucleoprotein. The dye did not cause appreciable displacement of protein from the DNA. With cetylpyridinium chloride the binding corresponded to about 41% of the DNA phosphates. With polylysine preparations of molecular weight 1250 and 7790 the binding values for deoxyribonucleoprotein were 46 and 38% respectively. The results suggest that the free phosphates lie in stretches sufficiently long to accommodate most of each polylysine molecule. With polylysine of molecular weight 62000 cross-linking of free stretches of DNA on different deoxyribonucleoprotein molecules probably occurs. It is concluded that although most of the free phosphates are probably ;hidden' beneath covering histone, corresponding perhaps to runs of non-basic residues in the latter, they are surprisingly accessible to very large molecules. The relevance of this finding to the problem of gene repression is discussed.

Animals↗
PubMed1984

Deoxyribonucleoprotein complexes and DNA synthesis of herpes simplex virus type 1.

Two temperature-sensitive mutants of herpes simplex virus type 1 in complementation group 1-1 were analyzed to determine if the major DNA-binding protein they produced was thermolabile. Cells infected with these mutants were analyzed for deoxyribonucleoprotein complexes containing the DNA-binding protein. These complexes were found in cells infected at the permissive temperature but not at the nonpermissive temperature. In temperature shift-up experiments with mutant virus infected cells, the levels of the deoxyribonucleoprotein complexes decreased with time of incubation at the nonpermissive temperature. Viral DNA synthesis terminated in cells infected with these mutants after temperature shift-up. The kinetics of termination of viral DNA synthesis were similar to the kinetics of dissociation of the deoxyribonucleoprotein complexes. These results indicate that two mutants in complementation group 1-1 produce a thermolabile DNA-binding protein and that this protein is required for viral DNA synthesis. Furthermore, they suggest that the major DNA-binding protein of herpes simplex virus type 1 functions in viral DNA synthesis as a component of deoxyribonucleoprotein complexes.

Animals↗
PubMed1976

Effects of irradiation on RNA synthesis primed by calf thymus deoxyribonucleoprotein treated with salt and salt-urea.

1. The effects of ionizing radiation on the activity of calf thymus templates were examined in a Escherichia coli RNA polymerase system. 2. The template activity of native and 2 M NaCl-5M urea-treated deoxyribonucleoproteins was enhanced by relatively low doses of irradiation, while that of 2 M NaCl-treated deoxyribonucleoprotein was not enhanced by irradiation. 3. The template activity of purified DNA was markedly decreased by irradiation, while that of native deoxyribonucleoprotein, 2 M NaCl-treated, and 2 M NaCl-5 M urea-treated ones were slightly decreased at a higher dose range. The doses for 50% inactivation of these templates were 1.3, 210, 140, and approximately 200 krad, respectively.

Animals↗
PubMed1983

Identification and characterization of deoxyribonucleoprotein complexes containing the major DNA-binding protein of herpes simplex virus type 1.

Nuclear extracts were prepared from cells infected with herpes simplex virus type 1 (HSV-1) and fractionated by sucrose gradient centrifugation to identify deoxyribonucleoprotein complexes involved in viral replication. Large amounts of an HSV-1 induced protein with a molecular weight of about 133,000 sedimented as a broad peak in the 25 S region of the gradient and cosedimented with 13 S DNA fragments. The sedimentation of both the protein and DNA decreased upon treatment of nuclear extracts with DNase. This result indicated that the protein and DNA were associated in deoxyribonucleoprotein complexes. The protein was identified as the HSV-encoded major DNA-binding protein ICP8 based on its molecular weight, its association with DNA in nuclear extracts, and its immunoprecipitation with monospecific antiserum and monoclonal antibody to ICP8. Deoxyribonucleoprotein complexes containing ICP8 could be immunoprecipitated from nuclear extracts. When DNA was extracted from these immunoprecipitates, fractionated by agarose gel electrophoresis, transferred to nitrocellulose paper, and hybridized to 32P-labeled HSV-1 or cell DNA, both HSV-1 and cell DNA sequences were identified. Cesium chloride gradient analysis of the immunoprecipitated DNA indicated that duplex DNA was present in the complexes. Thus, the major DNA-binding protein of HSV-1 is associated with both duplex HSV-1 and cell DNA in vivo.

DNA-Binding Proteins↗