[The nuclear desoxyribonuclease (DNAse) spectrum of normal rat thymus cells and after whole-body x-ray irradiation]. / Izuchenie spektra iadernykh dezoksiribonukleaz (DNKaz) kletok timusa krys v norme i posle obshchego rentgenovskogo oblucheniia.

Spectra of thymocyte nuclear DNAases of control and irradiated (4 Gy) rats have been investigated. Using the method of SDS-electrophoresis of nuclear proteins in DNA-polyacrylamide gel (PAAG) the authors managed to discover a number of polypeptides of 35, 32, 17.7, 17.2, and 16.4 kDA molecular mass possessing a DNAase activity. The enzyme of 35 kDA is only active in the presence of Ca2+ and Mg2+ ions. Nucleases of 32, 17.7, 17.2, and 16.4 kDA are active in the presence of Ca2+ ions and inactive in the presence of Mg2+ ions or in the absence of divalent cations. A simultaneous addition of Ca2+ and Mg2+ ions to the incubation medium causes a synergistic effect with respect to the manifestation of these DNAase activities. Nucleases of 32, 17.7, 17.2, and 16.4 kDa only emerge after the preliminary removal of histones by ion exchange chromatography on a column with CM-sephadex C-50. The enzymic activity of 32 kDA protein increases 60 min after irradiation and drops to the control value in 4 h. At the same time, the postirradiation increase in DNAase activity of a low-molecular weight enzyme group remains invariable throughout the entire period of observation (1-4 h). The preinjection of cycloheximide (CHI) prevents the postirradiation degradation of chromatin and, simultaneously, makes the enzymic activity, corresponding to 35 kDA protein, disappear at the electrophoregrams. The experiments with CHI permit to identify the given enzymic fraction as Ca/Mg-dependent endonuclease. This indicates the participation of normally pre-existing Ca/Mg-dependent endonuclease in implementing the process of chromatin enzymic degradation in the irradiated thymocytes.

[Outlook for the genetic engineering approach in radiobiology]. / Perspektivy genno-inzhernogo napravleniia v radiobiologii.

Present evidence on the use of genetic engineering methods in studying the molecular mechanism of radiation damage and repair of DNA, as well as radiation mutagenesis and carcinogenesis has been summarized. The new approach to radiobiological research has proved to be extremely fruitful. Some previously unknown types of structural disorders in DNA molecule have been discovered, some repair genes isolated and their primary structure established, some aspects of radiation mutagenesis elucidated, and research into deciphering the molecular bases of neoplastic transformations of exposed cells are being successfully investigated. The authors discuss the perspectives of using genetic engineering methods in radiobiology.

[Molecular mechanisms of interphase death of lymphoid cells. Distribution of nuclease attack sites in chromatin and kinetic complexity of DNA in PDN]. / Molekuliarnye mekhanizmy interfaznoi gibeli limfoidnykh kletok. Kharakter raspredeleniia mest nukleaznoi ataki v khromatine i kineticheskaia slozhnost' DNK v sostave PDN.

On the basis of a quantitative correlation between single--and double-helix fragments of different length within PDN, a study was made of the pattern of distribution of the sites, attacked by nuclease, in the chromatin. It was shown that under the effect of ionizing radiation products of enzymic digestion of the chromatin. It was shown that under the effect of ionizing radiation products of enzymic digestion of the chromatin accumulated in thymocytes due to internucleosome degradation were excised from randomly localized genome sites. The analysis of the reassociation curves did not reveal distinctions in the kinetic complexity of the fractions of PDN and total DNA.

Distribution of nuclease attack sites and complexity of DNA in the products of post-irradiation degradation of rat thymus chromatin.

The distribution of nuclease attack sites in chromatin has been studied on the basis of the quantitative relationship of the single- and double-stranded fragments of various lengths in the products of post-irradiation degradation of chromatin (PDN). It has been shown that in irradiated thymocytes internucleosome degradation of chromatin occurs and the products of the enzymic digestion of chromatin derive from randomly distributed genome areas accumulate. Analysis of the reassociation curves has not shown any differences in the complexity of the PDN fractions and total DNA.

Determination of some nuclear deoxyribonucleases in X-irradiated rat thymocytes.

The spectrum of nuclear nucleases in control and irradiated (4 Gy) thymocytes has been investigated. Using the method of SDS electrophoresis of nuclear proteins in 3H-DNA-polyacrylamide gels a number of polypeptides of MW. 35, 32, 17.7, 17.2 and 16.4 kDa possessing nuclease activity were found. The 35 kDa enzyme is only active in the presence of Ca2+ and Mg2+ ions. In response to cycloheximide injection (3 mg/100 g body weight) and irradiation, we did not detect the 35 kDa nuclease activity. Nucleases of 32, 17.7, 17.2 and 16.4 kDa are active in the presence of Ca2+ ions. The activities of these nucleases increases 60 min after irradiation. These nucleases were also found in the fraction of polydeoxyribonucleotide (PDN).

[Radiation protective properties of a synthetic antagonist of glucocorticoids RU 38486]. / Issledovanie radiozashchitnogo deistviia sinteticheskogo antagonista gliukokortikoidov RU 38 486.

Radioprotective properties of synthetic antiglucocorticoid RU 38,486 were investigated. It was demonstrated that this antagonist of glucocorticoids possesses radioprotective effect in vitro and in vivo systems. Radioprotective properties at molecular level exhibited in inhibition of postirradiation endonuclease activation and in prevention of internucleosome chromatin degradation. Involvement of cytosol glucocorticoid receptors in initiation of radiation-induced programmed cell death is discussed.

[Electron microscopic analysis of postradiation apoptotic death of thymocytes and peripheral blood lymphocytes]. / Elektronno-mikroskopicheskii analiz postradiatsionnoi apoptoticheskoi gibeli timotsitov i limfotsitov perifericheskoi krovi.

Some stages of the apoptotic death of lymphoid cells (thymocytes and peripheral blood lymphocytes) have been followed up using light and electron microscopes. Differences have been revealed in the formation of death stages under natural physiological conditions and after gamma-irradiation. High radiation doses are shown to interfere with the process of nuclear chromatin condensation characteristic of the natural physiological death of cells.

[Mechanism of thymocyte death in exposure to ultrahigh doses of gamma radiation]. / Issledovanie mekhanizma gibeli timotsitov pri vozdeistvii sverkhvysokikh doz gamma-izlucheniia.

A comparative study was made of the morphological and biochemical indices of rat thymus cells after gamma-irradiation with doses of 4-10 Gy (median), 20 Gy (high), and 200-400 Gy (superhigh). It was shown that 4 h after irradiation with superhigh doses the yield of polydeoxynucleotides (PDN) was twice as low as that observed after doses of 4-10 Gy. 24 h after irradiation the amount of the extracted PDN in thymocytes exposed to superhigh doses was markedly larger than that after 4 hours. After all doses applied chromatin degradation occurred at the internucleosome sites in a strict order, the activity of acid and alkaline nucleases being unchanged. A large number of cells have normal nuclear structure 4 h after irradiation (200-400 Gy), as was demonstrated by the electron microscopy data, while in 24 h no intact cells were virtually found in the thymus which correlated with the changes in the PDN yield. The mechanisms of the lymphoid cell death under the effect of different radiation doses are discussed.