[Restoration of DNA supercoiling in fibroblasts in the rat subjected to gamma ray or fast neutrons].

Nucleoid sedimentation analysis was applied to the study of DNA supercoiling repair in cultured FR 3T3 fibroblasts exposed to low doses of fast neutrons or gamma-rays. Supercoiling was fully restored in both instances upon post-irradiation at 37 degrees C, but the rate of repair of neutron-induced lesions was lower than that for gamma-rays. Non-repairable breaks were not evidenced at the neutral pH used. We suggest that the non-repairable alkali-labile sites evidenced by others in neutron-irradiated DNA do not prevent strand break rejoining and subsequent recovery of the tertiary DNA structure.