An alkaline deoxyribonuclease from rat liver non-histone chromatin proteins

Brain protein changes during development and sexual differentiation in the rat

Subcellular fractions were prepared from the hypothalamus-preoptic area and the 'remainder of the brain' of intact male and female rats at 0, 8, 25 and 72 days of age. Proteins associated with each fraction were subjected to SDS-PAGE chromatography and stained with Coomassie Brilliant Blue. Developmental changes were found to occur in proteins associated with the soluble (14,600, 15,000, 29,900, 38,900 and 49,000 mol. wt), nuclear (40,000-50,000 and 13,800-16,000 mol. wt.), mitochondrial-lysosomal (49,000-52,000 mol. wt.) and microsomal (14,400, 20,000, 50,100, 56,900 and 130,000 mol. wt.) fractions. In addition, soluble proteins were greater in males than in females at days 0 (53,000-56,000 mol. wt.; probably tubulin) and 25 (14,600 and 15,000 mol. wt.). These changes in brain proteins probably reflect important structural and functional changes that occur during maturation and sexual differentiation of the brain.

Involvement of deoxyribonuclease activity in the differential sedimentation rates of nucleoids from non-transformed and transformed mouse embryo fibroblasts

Lysis of non-transformed confluent C3H10T1/2C18 mouse embryo fibroblasts in the presence of detergents, high concentrations of salt and EDTA on top of neutral sucrose gradients revealed a reduced sedimentation rate of the resulting nucleoids from these cells compared to those from exponentially growing non-transformed cells or from transformed cells. Exposure of confluent cells to 1000 rads of X-ray had no effect on this rate of nucleoid sedimentation; and ethidium bromide titration and alkaline sucrose analysis suggested the presence of discontinuities in the DNA. An endonucleolytic activity could be extracted from nuclei of these cells with 0.5 M NaCl, indicating a very tight association with the chromatin. Such an enzyme in non-transformed confluent cells may account for the differences in nucleoid structure and may be related to changes in cell function with normal arrest of cell growth. There was no growth-phase effect on the properties of nucleoids from transformed cells.

Purification and some properties of a deoxyribonucleic acid endonuclease endogenous to rat liver chromatin

A deoxyribonucleic acid (DNA) endonucleolytic activity has been purified from a 0.3 M KCl extract of rat liver chromatin by a combination of selective precipitation and ion-exchange and gel filtration chromatography. The purified protein has a molecular weight of 35 000 as determined by Sephadex G-200 gel filtration and sodium dodecyl sulfate-acrylamide gel electrophoresis. The nuclease activity is stimulated by the addition of Mg2+ and thus may represent the Mg2+-activated DNase endogenous to chromatin. The purified enzyme has the ability to make both single-strand nicks and double-strand cuts in DNA.

Purification and properties of a nuclear DNA endonuclease from HeLa S3 cells

An endonuclease that can act on calf thymus DNA and circular doublestranded phage PM2 DNA has been isolated from HeLa S3 cell chromatin. Approximately 200-fold purification was achieved by a sequence of subcellular fractionation, differential NaCl solubility and chromatography on CM-Sephadex, DEAE-cellulose and hydroxyapatite, and isoelectric point is pH 5.1 +/- 0.2. Divalent cations are necessary for its activity and the enzyme is heat inactivated at 60 degrees C. The enzyme activity is sensitive to caffeine and sulfhydryl reacting compounds. The molecular weight, determined by gel filtration and SDS gel electrophoresis, is approx. 22 000.

Correlation between deoxyribonuclease activity and DNA replication in the embryonic axes of germinating peas (Pisum sativum L.)

Crude chromatin preparations from pea seedlings contain calcium-dependent deoxyribonuclease activity, at least part of which is endonucleolytic. During germination, there is a dramatic increase in chromatin-bound deoxyribonuclease activity in the embryonic axis immediately prior to the onset of DNA replication. Evidence has been obtained for the presence of an inhibitor of deoxyribonuclease activity in chromatin preparations from embryonic axes not undergoing DNA replication.

Specific interaction of chromatin non-histone proteins with DNA

The interaction of different preparations of chromatin non-histone proteins of rat liver and thymus with homologous and heterologous DNA was studied. It is shown by the method of fixation of non-histone proteins-DNA complexes on nitrocellulose filters that: (1) all the non-histone proteins preparations studied form complexes with DNA in 0.02 M Tris--HCl (pH 7.5)--3 mM MgCl2; (2) the main part of non-histone proteins interacting with DNA binds to it non-specifically; (3) a small part of non-histone proteins interacts specifically with the homologous native DNA in 5 M urea; (4) both homologous and heterologous denatured DNA binds non-histone proteins more effectively than the native one; (5) the specific interaction of non-histone proteins with the homologous denatured DNA is observed both without urea and in its presence. The specific interaction of a small part of non-histone proteins with the homologous native and denatured DNA is also shown by the method of non-histone proteins chromatography on polyacrylamide--agarose columns containing DNA. The data obtained are discussed in the light of the possible non-histone proteins role in the specific regulation of the transcription process.

[Morphological and biochemical characterization of the developmental stages of fertilized eggs inSphaerechinus granularis Lam : II. DNA content, DNA polymerase activity and DNase activity]

The investigations were performed with the eggs of the sea urchin speciesSphaerechinus granularis Lam. They were kept at 22° C under continuous aeration for up to 45 hours with stirring to compensate for sedimentation. 1. The change in DNA content, 2. the change in DNA dependent DNA polymerase activity, and 3. the change in DNase activity with time have been evaluated. 1. DNA Content of Embryos. The DNA content of the embryo development was determined by two different methods. Before and immediately after fertilization DNA content has been found to be 1.7±0.5·10^-10 g per egg. This amount is about 100 times higher than in diploid nuclei. Three periods with different rates of DNA synthesis may be distinguished: a) the first one, lasting from fertilization to about the time of the volume maximum just before the onset of gastrulation with an average rate of synthesis of 1.2·10^-10g DNA per minute per embryo; b) a second one, lasting from then on to the gastrula stage with a lower average rate of synthesis of about 0.7·10^-12 g DNA per minute per embryo; c) a third one, starting from the gastrula stage up to the experimental end point in the pluteus stage. The rate of synthesis in this case is 2.3·10^-12 g DNA per minute per embryo. On a relative base the rates of synthesis are 100∶58∶192. The cytoplasmic, extramitochondrial DNA persists through the stage of the first period of the embryogenesis, up to the blastula stage. The amount of extranuclear DNA increases in the first 6 hours of embryo development; then the cytoplasmic DNA disappears. 2. DNA Dependent DNA Polymerase Activity. The DNA polymerase has been isolated from embryos. Its activity has been determined in relation to the activity of the total embryo as well as per embryonic cell. The polymerase activity is much higher at the start of the development than in later stages, reaching a minimum in the blastula stage, the time at which cytoplasmic DNA has been exhausted. In the subsequent period the polymerase activity parallels the rate of DNA synthesis in vivo. The level of the DNA polymerase activity per cell remains constant. 3. DNase Activity. The DNase activity has been determined using the Lanthanum-Nitrate-Method. Three distinct maxima were found: A first maximum is reached immediately upon fertilization. The second one coincides with the onset of mesenchyme formation in the blastula, and the third one coincides with the end of gastrulation. The average specific activity is roughly equivalent to about 10^-6 g DNase I per g of embryo. The possibility is discussed that rises in nucleolytic activities may trigger differentiation events in the developing egg. The influence of DNA polymerase activity and DNase activity on in vivo DNA synthesis is discussed.