Formation of strand breaks in the DNA of gamma-irradiated chromatin.

Strand breaks have been determined by sedimentation on sucrose gradients in the DNA of chromatin irradiated after isolation from Chinese hamster lung fibroblasts. The yields of double-strand and single-strand breaks are similar to those found in the DNA of irradiated mammalian cells. Irradiation of isolated chromatin in the presence of the radical scavenger tertiary butanol indicates that at least 65% of single-strand breaks and 56% of double-strand breaks can be attributed to the action of hydroxyl radicals. The results indicate the influence of chromosomal proteins in modifying radiation damage to DNA and suggest that the mechanisms for the induction of strand breaks in the DNA of isolated chromatin may be comparable to those operating in the intact cell.