[Effect of 5-deoxy-5-S-isobutyladenosine on the synthesis and methylation of DNA in mouse lympholeukemia cells and human lymphocytes].
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Animals↗
Biomedical subjects
B F Vaniushin
Publications and source records attributed to B F Vaniushin.
[Quantitative spectrophotometric determination of non-identified nucleotides in DNA].
A method for calculation of molar extinction coefficients (epsilon) and for quantitative spectrophotometric determination of non-identified nucleotide analogs from nucleic acids of some bacteriophages is proposed. The method is based on spectral properties of known and unknown nucleotides and of their dinucleotide isolated from the DNA studied.
Coliphages↗
[Changes in DNA methylation in alfalfa plants infected with Cuscuta and tissue differences in DNA methylation of the parasite plants].
The tissue-specific differences in the 5-methylcytosine (m5C) content in total DNA of the parasite plant Cuscuta reflexa have been found: DNA from apical parts of the plant is less methylated (m5C = 4,2 mol %) as compared to the DNA from haustoria and posthaustorial regions (m5C = 5,4 mol %). The base compositions of total DNA preparations from C. reflexa grown on various hosts are similar. The m5C amount in stem DNA of the alfalfa plant infected with C. reflexa is by approximately 25% higher than that in the non-infected plant DNA. The GC content in alfalfa DNA does not change as a result of infection. Thus, the parasite induces the hypermethylation of DNA in the host plant. It is assumed that the changes in DNA methylation induced by the parasite plant may play a regulatory role and may cause changes in transcription and replication of host DNA.
Cytosine↗
[Interaction of rat liver dexamethasone-receptor complexes with DNA].
Rat liver glucocorticoid-receptor complexes (GRC) acquire the ability to bind to DNA in a high affinity manner after activation by heating or precipitation with (NH)2SO4. DNA is practically non-saturable by GRC in low salt buffers as well as in 0.15 M NaCl-containing buffer, although in the latter case the binding decreases approximately 3--5 times. GRC bind to homo- and heterologous prokaryotic DNA in a similar way; in both cases an addition of KCl (up to 0.15 M) to the medium is followed by the same decrease of the binding. This data suggest that the association of GRC with DNA observed in vitro is not accompanied by "recognition" of any certain DNA site. Besides DNA, activated GRC can associate with other polymers, charged positively (DEAE-cellulose) or negatively (RNA, polyvinylsulfate). GRC interact very weakly with neutral compounds of the cellulose type but are strongly adsorbed on hydroxyapatite. Hence the activated GRC can be considered as an amphoteric protein. Salt solutions provoke dissociation of the GRC-DNA triple complexes: a complete dissociation is observed in the presence of 0,4 M NaCl or 0,4 M sodium phosphate buffer (pH 6,9). Sodium phosphate buffer also elutes GRC from other sorbents such as DEAE-cellulose or hydroxyapatite. No significant dissociation of the GRC-DNA complexes is observed at sucrose concentration up to 2 M. The data obtained are indicative of an essential role of electrostatic forces for the interaction of GRC with DNA. The non-ionic detergent Triton X-100 at a concentration as low as 0,05% completely destroys the GRC-DNA triple complexes. The models explicating the selectivity of the genome activation by GRC without their "recognition" of any specific DNA sequences are proposed.
Animals↗
[Tissue specificity of the decrease of cattle lymphocyte DNA methylation during chronic lymphoid leukemia].
It has been found that the content of m5C in the DNA preparations tested have been revealed. The DNAs from normal and leukemic lymphocytes of blood, lymphonodi and spleen differ in ther acceptor ability in the reaction of heterologous methylation in vitro, induced by DNA-methylase from Enterobacter cloacea in the presence of [3H-methyl]S-adenosyl methionine: the ratio of radioactivities in methylated cytosine and adenine residues (m5C/m6A) in leukemic lymphocyte DNA is much lower than in healthy animals' lymphocytes. The decrease in the methylation of DNAs from various lymphoid organs of animals with chronic lymphoid leukemia is well correlated with the impairment. No significant changes of the m5C level and the acceptor ability of the in vitro reaction of heterologous methylation of cow lymph lymphocyte DNA have been observed. The data obtained may be interpreted in terms of tissue (cell) specificity or differences in the degree of DNA methylation under conditions of chronic lymphoid leukemia. It is assumed that the changes in DNA methylation may underlie the disturbances in the regulation of activity of the leukemic cell genetic mechanisms.
Animals↗
[Methylation of newly synthesized DNA in mouse fibroblast culture].
After a 10 min- or more prolonged incubation of transformed mouse fibroblasts (L.-cells) with [3H]-thymidine or [3H-methyl]-methionine and a subsequent centrifugation of cell lysates in an alkaline sucrose gradient the DNA radioactivity is detected in long (28, 33 and 45S) and short (5, 13 and 18S) fragments. An increase in cell concentration in the cultural layer results in inhibition of 5S fragments linkage rather than in inhibition of their synthesis. The blocking of the Okazaki fragment linkage may be regarded as one of the inhibitory molecular mechanisms of cell depletion. Both in the case of normal and suppressed (by 99%) replication by arabofuranosylcytosine [3H]-thymidine and [3H-5-methyl] cytosine are detected in the Okazaki fragments (5S) as well as in some discrete lower molecular weight fractions (lesser than 5S) of newly synthesized DNA. Thus, replicative methylation of DNA in the fibroblasts occurs in the replicative fork during DNA synthesis and the functioning DNA methylase is an indispensable component of the replicative complex. The methylation of Okazaki fragments is non-chaotic and has a specificity other than that of total DNA. This may be due to the multiplicity and different specificity of nuclear DNA-methylases. Thus, there exist in animal cells replicative and post-replicative methylation of DNA, which may differ in the nature of substrates and enzymes, in specificity of recognizable sequences and in their functional significanse.
Animals↗
[Correlation of the increase in DNA methylation and antioxidant activity of mouse liver nuclear lipids after administration of antioxidant and in Ehrlich ascites carcinoma].
The content of 5'-methylcytosine in total DNA of mouse liver increases 2--2,5-fold 3 hrs after a single intraperitoneal injection of antioxidant (4-methyl-2,6-ditretbutylphenol) (20 or 60 mg per 1 kg of body weight) and makes up to 2--2.4 mol.%. The methylation of liver DNA is also increased more than 2-fold in Ehrlich ascite carcinoma. The DNA isolated from mouse liver after administration of antioxidant or during cancer growth markedly differs from liver DNA of intact animals in its CH3-accepting ability under in vitro methylation by the methylase complex from Enterobacter cloacea. The changes in DNA methylation in mouse liver under the effects of antioxidant and in Ehrlich ascite carcinoma are correlated with the changes in the antioxidant activity of liver nuclear lipids.
Animals↗
[Age- and tissue-specific differences in intragenome distribution of 5'-methylcytosine in cow's DNA].
In aged animals the content of 5'-methylcytosine (m5C) in total thymus DNA (1,29 mol.%) and heart muscle (1,10 mol.%) is decreased by 30 and 40%, respectively as compared to that in the 8-months-old embryos. No differences in the GC-content and reassociation kinetics of these DNAs have been revealed. Consequently, the age differences in the m5C content are caused by the decrease in DNA methylation upon ageing. The degree of DNA methylation in various organs (thymus, heart) is different. Upon ageing the degree of genome methylation is decreased and the pattern of methylation is changed: the m5C content is decreased in the repeated sequences and remains practically unchanged in the unique ones. The level of methylation in thymus DNA of moderately (C0t = 4--400) and highly (C0t less than 4) repeated sequences is thereby decreased almost in the same degree. In heart DNA of aged cows the hypomethylation of highly repeated sequences is more pronounced as compared to the moderately repeated ones. The age- and tissue-specific decrease of DNA methylation is regarded as a possible mechanism responsible for the decrease of transcription and functional activity of the cells upon ageing.
Aging↗
[Intragenome distribution of 5-methyl cytosine and reassociation kinetics of cow blood lymphocyte DNA under normal conditions and in chronic lymphoid leukemia].
The DNA from cow blood lymphocytes is methylated in a varying degree: the maximal content of 5-methyl cytosine (2,3 mol%) is found in the "instantly" renaturating sequences (Cot lett than 10(-4)), a relatively large amount (1,4 mol%)--in moderately repeated sequences (Cot = 10(-4)--400) and the minimal amount (0,9 mol%) in the unique sequences (Cot greater than 400). In their reassociation kinetics, GC-content and other physico-chemical properties the blood lymphocyte DNA of the controls and of animals with chronic lymphoid leukemia appear to be similar. Consequently, the genome organization of leukemic animals does not change significantly; a considerable decrease of 5-methyl cytosine of lymphocyte DNA in lymphoid leukemia parallels the decrease of genome methylation in the leukemic cells. This decrease does not affect the unique sequences, but involves all types of repeated sequences (moderately and frequently repeated ones and palindromes). It is assumed that the specific disturbances in genome methylation under lymphoid leukemia may be a cause of transcription deficiences and cell transformations.
Animals↗
[Reaction between dexamethasone-receptor complexes and DNA as the basis for their translocation into the cell nucleus in vivo].
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Animals↗
[On the impossibility of the incorporation of 5-methylcytosine and its nucleosides into higher plant DNA].
No radioactivity was detected in 5-methylcytosine isolated from wheat DNA after incubation of wheat seedlings with 3H-labelled 5-methylcytosine, 5-methylcytidine and 5-methyldeoxycytidine. No label from 3H-5-methylcytosine was found in DNA of seedlings. After incubation of seedlings with 3H-labelled nucleosides of 5-methylcytosine, radioactivity was discovered only in thymine of DNA. Thus 5-methylcytosine and its nucleosides can not be used in plants as direct precursors of 5-methyl cytosine residues in DNA, but nucleosides of 5-methylcytosine may be deaminated to thymidine (or deoxythymidine) and subsequently incorporated into DNA.
Cytidine↗
[Changes in 5-methylcytosine content of plant DNA in proportion to the amount of flowering].
A study has been made of the content of GC pairs and 5-methylcytosine in the total DNA of generative (inflorescences, flowers, flower buds) and vegetative (shoots, leaves, vegetative buds) organs in pea, tobacco and apple due to flowering gradient. In all the plants studied, the content of 5-methylcytosine in the DNA of generative organs in high as that in the DNA of vegetative organs. The DNA from various organs of one and the same plant hardly differs by the GC content. The differences in the amount of 5-methylcytosine are probably indictive of various levels of DNA methylation. Thus tissue (cell) DNA of both plants and animals differs in the content of 5-methylcytosine. Besides, methylation of genome in them changes upon flowering, i.e. we revealed the gradient of the degree of methylation of plant genome which correlates positively with the known flowering gradient. Methylation of plant genome regulated by phytohormone is possibly associated with cell differentiation and may be considered as being one of the mechanisms of regulation of transcription.
Cytosine↗
[Distribution of 5-methylcytosine in pyrimidine oligonucleotides of higher plant DNA].
The level of pyrimidine clusters (isopliths) and distribution of 5-methylcytosine in DNAs of some archegonial (ferns, ginkgo) and flowering (cordyline, tulip, wheat) plants has been studied. DNA from Cordyline australis (Liliaceae) is one of the GC-type (GC = 57.5 mol.%), has very low methylation level (amount of m5C is about 1 mol.%) and significantly differs from other species DNAs studied in terms of pyrimidine distribution patterns, i.e. amount of dipyrimidine fragments is higher than that of monopyrimidine ones. All other plant DNAs under study are of the AT-type, have similar pyrimidine distribution patterns and are characterized by high degree of pyrimidine blocking; specific differences in the level (approximately 10-fold) and type of genome methylation are found. In all DNAs studied 5-methylcytosine is unevenly distributed in pyrimidine isopliths: the degree of cytosine methylation [m5C(C+m5C)] is decreased with an increase in the length of isopliths, irrespective of the ratio of thymine and cytosine residues. 5-methylcytosine is mainly accumulated in mono- and dipyrimidine fragments (60--68%). Specific differences in 5-methylcytosine content in trinucleotides and long-chain pyrimidine oligonucleotides are revealed.
Cytosine↗
[Localization of (3H)hydrocortisone in rat liver nuclei].
The content of hydrocortisone in rat liver nuclei reaches its maximum in 1 hour after its intravenous injection and remains stable for another hour. In three hours after introduction it falls to the initial level (15 min after the injection of [3H]hydrocortisone). The accumulation of the hormone in nuclei completely coincides with kinetics of reversible DNA supermethylation and correlates with the induction of transcription. No free [3H]hydrocortisone was found in nuclei, in isolated nuclei it is found in the fraction of nuclear membranes, nucleoplasma, nucleolus and chromatin. Specific radioactivity of [3H]hydrocortisone (d. p. m. per 1 mg of DNA) in active chromatin is 10--50-fold as high as in condensed chromatin and is 10--15-fold as high as in nucleolus. It is suggested that there are at least two types of binding hormonereceptor complexes with chromatin. The initial binding of these complexes with condensed chromatin may result in its structural rearrangement (euchromatization), in the appearance of more specific secondary sites for binding hormone-receptor complexes with chromatin DNA, and also in the appearance of methylation and transcription initiation sites in DNA.
Animals↗
[Tissue-specific decrease and change in the character of DNA methylation in cattle with aging].
The content of 5-methylcytosine (m5C) in DNA of different cow organs is found to decrease in ontogenesis. No other age changes were found in DNA structure and molecular population (GC content, the content of different in the length and the base composition pyrimidine clusters, hyperchromicity value etc.). It is suggested that the age tissue-specific decrease of the m5C content is due to a decrease of the level of DNA methylation, which takes place in heart, kidneys, spleen and brain DNAs and is not observed in lungs. Maximal level of DNA methylation was observed at embryogenesis, when the m5C content in heart DNA decreases (from 1.8 to 1.4 mol. %), then it remains stable up to 1 year old and then sharply decreases with age and reaches 0.94 mol. % at the age of 10 years. The m5C content in liver DNA decreases (from 1.6 to 1.2 mol. %) at the end of embryogenesis and then it does not change. A pronounced decrease of the m5C content was observed in DNAs of cerebral hemispheres, cerebellum, hyppocampus, neurohypophysis and thymus. The decrease of m5C content in thymus DNA is non-random, it concerns only Pu-m5C-Pu, but not long pyrimidine clusters Pu-Pyn-Pu (n greater than or equal to 2). Tissue-specific decrease and the change in pattern of DNA methylation observed are suggested to be a possible mechanism for the age change (distortion) of transcription and cell functioning.
Aging↗
[Replication and reassociation kinetics of nuclear matrix DNA from regenerating rat liver].
Fraction 1, containing 65--70% of nuclear DNA (nDNA) was extracted from isolated rat liver nuclei. Then nuclear matrix fraction, containing 30--35% of nDNA was extracted with 1.2 M NaCl. About 1% of nDNA war discovered in residual matrix. Specific activity of residual matrix labelled DNA within 1 and 3 min. after the injection of 14C-orotic acid into the liver portal vein (24 hours after hepatectomy) was respectively in 70 and 50 times higher, and that of matrix DNA--in 45 and 20 times as high as in fraction 1 DNA. Thus, replication begins from nuclear matrix DNA. The latter is enriched with unique sequences by 10%, as compared with total nDNA, and its reassociation kinetics does not change at different stages of the cell cycle (0 and 24 hours after partial hepatectomy). It is suggested, that DNA does not migrate with respect to nuclear matrix under replication.
Animals↗
[Changes in the specificity of DNA methylation in cattle blood lymphocytes under chronic lymphoid leukemia].
Under conditions of chronic (spontaneous) lympholeucosis the amount of 5-methylcytosine in cattle blood lymphocyte DNA is decreased approximately by 30%. No other changes in the DNA (e. g. GC-content, Tm, amount of pyrimidine sequences differing in their lengths and composition) were observed. Thus, the decrease in the amount of 5-methylcytosine in lymphocyte DNA is due to a decrease in DNA methylation. This decrease is non-random and involves mainly the Pu-m5C-Pu sequences without affecting the long pyrimidine blocks. In nuclear extracts from lymphocytes of healthy animals the DNA-methylase activity having an optimum at pH 6,0 was found; the DNA-methylase activities found in the nuclear extracts of leukaemic cow lymphocytes had their optima at pH 5,5 and 7,5. In vitro the DNA-methylase activities of leukaemic lymphocytes nuclei methylate the cytosine residues of DNA in other sequences than enzyme(s) of the extracts from normal lymphocyte nuclei. Changes in the pattern of DNA-methylase activities as well as the decrease and distortions in the character of DNA methylation may underlie the disturbances in the regulation of transcription of genome and cause the transformation of cells under conditions of lympholeucosis.
Animals↗
[Level of methylated nuclear DNA in neurons and glia of rat cerebral cortex and its alteration upon elaboration of a conditioned reflex].
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Animals↗