X-Ray-Induced DNA Double Strand Breaks in Polynucleosomes

Abstract

Most of the studies on DNA damage induced by ionizing radiations are based on the assumption that lesions are randomly distributed along the cellular DNA. However, Roti Roti et al. reported that the efficiency of gamma radiation in producing DNA thymine damage (tγ) depends on the amount of proteins associated with DNA (1). Since chromatin structure is not uniform in the genome and changes during replication and transcription, it seems reasonable to assume that different DNA regions may have different radiosensitivity. In fact, a non-random distribution in DNA damage was recently found by some authors. after gamma irradiation, Chiu et al. (2) observed that both single strand breaks (ssb) production and repair were greater in actively transcribing genes than in total nuclear DNA. Warters and Childers (3) found that the newly replicated DNA was hypersensitive to the induction of tγ-type damage. These findings have been related to the different accessibilities of DNA regions to diffusible radicals and repair enzymes, and point out the importance of the association of DNA with the protein component of chromatin.