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It was shown that the buoyant density of DNA isolated from lymphocyte incubation media as well as from blood plasma of healthy patients and patients with chronic lympholeukemia (CLL) using the SDS-phenol method with subsequent ultracentrifugation in a cesium trifluoroacetate density gradient is 1.59-1.60 and 1.60-1.63 g/ml, respectively. Using electrophoresis in 0.6% agarose gel, it was found that the DNA excreted by lymphocytes from healthy patients and CLL patients is a high molecular weight fraction comprising 21,000 nucleotide pairs. This DNA fragment contains 90-95% of [3H]thymidine used for the labeling of DNA excreted by lymphocytes from healthy patients and patients with CLL. No traces of [3H]thymidine were found in the middle part of the agarose gel containing the diffuse material bound to ethidium bromide.

Possible use of ethidium bromide immobilized on polyacrylamide gel for DNA extraction from biological media, e.g., cell lysates and blood serum, is discussed. The ability of the affinity gel to cause fractionation of single- and double-stranded DNA is demonstrated.

In vitro and in vivo studies showed that methylation of homologous DNA in nuclear homogenates of rat bone marrow is controlled by cyclic nucleotides and some hormones. The cyclic nucleotides and their dibutyryl analogs inhibited homologous methylation of DNA in the presence and absence of phosphodiesterase inhibitors. In the presence of Ca2+ the inhibiting effect of the nucleotides was more pronounced. Prostaglandins inhibited DNA methylation in a weaker degree while insulin and erythropoietin had a stronger effect in comparison with the nucleotides. Histamine stimulated DNA methylation, whereas acute hypoxic hypoxia caused a reduction in the rate of DNA methylation.

A method for determination of DNA sedimentation profiles in density gradients of sucrose or salts is proposed. The method consists in isolation and purification of DNA from the fractions by molecular filtration and a subsequent determination of DNA content by the fluorescence of the DNA-ethidium bromide complex.

Protein composition of chromatins from the liver of various Vertebrates (frog, turtle, hen and rat) has been compared by the immunological method of double diffusion in gel. It was shown that non-histone chromosomal proteins and histones exhibit evident species specificity.

Methylation of pyrimidine isoplythes of newly synthesized DNA from activated human blood lymphocytes was studied under normal conditions and in chronic lymphocytic leukemia. The analysis of distribution of labelled 5-methylcytosine in DNA pyrimidine oligonucleotides, differing in their lengths, showed a considerable increase in the methylation of pyrimidine oligonucleotide fragments of DNA from lymphocytic leukemia lymphocytes as compared to normal. The greatest differences were observed in methylation with respect to longer fragments, e.g. under chronic lymphocytic leukemia the level of methylation of the cytosine residues of DNA in isoplythes I and II, as well as in the fraction of isoplyth III and in longer fragments exceeded that of the normal DNA isoplythes, 3.7-, 2.1- and 8.3-fold respectively.

Fluorometric measurements of the levels of radiation injury to DNA of leucocyte lysates were made on the basis of the estimates of alkaline denaturation rate obtained by the method of Birnboim and Jevcak. Leucocytes of human blood in vitro and rats were exposed to doses of 0.5, 1, 1.5, 3, 6 and 9 Gy. It was shown that the percentage of double-stranded DNA of leucocytes of irradiated human blood decreased with the increase in the radiation dose while that of exposed rats decreased immediately after irradiation and was normalized after 20 h.