RESUMO
In the present paper experimental results from radiobiological investigations of the sedimentation behaviour of damaged and restored DNA-subunits attached to the nuclear membrane have been summarized. The studies were carried out preferably with Chinese Hamster cells V79-4 irradiated with different kinds of radiation (gamma-rays, neutrons and carbon ions) using the nucleoid sedimentation technique. Single-strand breaks relax the supercoiled DNA in the subunits resulting in a decreased sedimentation velocity. Rejoining leads to a correct restoration of the structure as can be studied by means of postincubation irradiation. Double-strand breaks release DNA fragments, again leading to an increased sedimentation velocity. If the average number of the induced double-strand breaks per subunit increases to a number higher than one, the measured results suggest that the structures should not be restored completely. The results are compatible with a new repair model developed in our laboratory on the assumption that, firstly, the single DNA subunits are the sensitive target rather than the whole DNA and, secondly, the repair of DNA damage takes place independently in each subunit.
Assuntos
Dano ao DNA , Reparo do DNA , DNA/efeitos da radiação , Raios gama , Íons , Nêutrons , Animais , Carbono , Carcinoma de Ehrlich/química , Carcinoma de Ehrlich/patologia , Linhagem Celular , Cricetinae , DNA/análise , DNA/química , DNA de Cadeia Simples/efeitos da radiação , DNA Super-Helicoidal/efeitos da radiação , Relação Dose-Resposta à Radiação , Humanos , Transferência Linear de Energia , Linfócitos/química , Linfócitos/citologia , Linfócitos/efeitos da radiação , Camundongos , Modelos Biológicos , Radiobiologia , Células Tumorais CultivadasRESUMO
The sedimentation behaviour of DNA-protein complexes was studied following irradiation of Chinese hamster cells (V79-4) and human lymphocytes over a wide dose range of 137Cs gamma-rays, pulsed neutrons and accelerated 12C ions. We have shown that the decrease of relative sedimentation velocity of the complexes at low doses is related to the occurrence of single-strand breaks in DNA. Rejoining of the breaks during a repair period increases the sedimentation velocity. At higher doses of radiation, double-strand breaks lead to an increase of sedimentation velocity of DNA-protein complexes. A new method can be devised on the basis of these results enabling estimation of the yields of single- and double-strand breaks in DNA.
