Repair of a DNA Complex from X-irradiated Chinese Hamster Cells

Abstract

Using velocity sedimentation in alkaline gradients of the DNA from Chinese-hamster cells, damage and repair processes were studied as a function of x-ray dose. DNA-containing material released by alkaline lysis is initially contained in a complex-containing lipid, the sedimentation of which is anomalous relative to denatured DNA from unirradiated cells. Doses of x-rays small enough to be in the range that permits high survival (i.e. 100 to 800 rads) speed the resolution of single-stranded DNA from this DNA complex, giving rise to a species having a number average molecular weight of 2 × 10⁸ dalton. Large doses—greater than 1000 to 2000 rads—result in degradation of these DNA strands. Incubation after irradiation results in the rapid repair of both forms of damage, although the rate of repair of damage to the complex decreases with increasing dose. Repair of radiation damage to the complex results in a re-association of lipid and DNA. The evidence supports the possibility that a large DNA-membrane structure is a principal target of radiation.