M. Kapiszewska et al., DAMAGE AT 2 LEVELS OF DNA FOLDING MEASURED BY FLUORESCENT HALO TECHNIQUE IN X-IRRADIATED L5178Y-R AND L5178Y-S CELLS .2. REPAIR, Radiation and environmental biophysics, 33(1), 1994, pp. 35-44
Citations number
36
Categorie Soggetti
Biophysics,"Radiology,Nuclear Medicine & Medical Imaging","Environmental Sciences
In the preceding paper we described the properties of nucleoids analyz
ed with the fluorescent halo assay at pH 6.9 and 9, as well as in the
presence of reducing and chelating agents and after X-irradiation. We
found analogies between the properties of type I and II nucleoids, as
examined by Lebkowski and Laemmli (1982), and nucleoids analyzed with
the fluorescent halo assay. We concluded that radiation-inflicted dama
ge at two levels of DNA folding is measured at pH 6.9 and 9. In this p
aper we examined repair of damage to the nucleoid structure as assayed
by the fluorescent halo method in X-irradiated L5178Y (LY) sublines;
R (radiation resistant, D-0=1.4 Gy) and S (radiation sensitive, D-0=0.
5 Gy). Halo diameters were measured after cell lysis in the presence o
f propidium iodide (PI; 0.5 to 50 mu g/ml) at pH 6.9 and 9. The abilit
y of DNA to be rewound at 10-50 mu g/ml of PI was impaired by X-irradi
ation and partly restored during 90-min post-irradiation incubation, i
ndicating damage to the superhelical structure and its partial restora
tion. The exponential time constants for repair were 10.1 min (LY-S, 6
Gy), 11.2 min (LY-R, 12 Gy), and 20.3 min (LY-s, 12 Gy) when measured
at pH 9. In X-irradiated (12 Gy) LY-S cells, slower restoration of DN
A supercoiling was observed at pH 9 than at pH 6.9. The presence of la
bile lesions at pH 9 did not prevent restoration of the higher-order D
NA structure, as estimated from DNA rewinding at pH 6.9 in LY-S cells.