Intrachromosomal localization of aberration breakpoints induced by neutrons and gamma rays in Chinese hamster ovary cells.

Chromosome breakpoints induced by neutrons or gamma rays in Chinese hamster ovary cells were mapped to Giemsa-light or Giemsa-dark bands or to band junctions. Radiation-induced breakpoints were found to be distributed nonrandomly according to chromosome or band length. More than 60% of the breakpoints were localized in G-light bands. A group of 13 bands which corresponded to only 7% of the total chromosome length contained 22% of the breakpoints produced by neutrons and 14% of those induced by gamma rays. Seven of these 13 bands are also preferentially damaged by AluI, BamHI and DNase I as reported previously. The results indicate that chromatin and nuclear structure may play a role in the distribution of breakpoints produced by ionizing radiation and endonucleases.