Chromosome aberration types in cells irradiated in G1 with nutrient depletion.

When cultured JU56 cells were blocked in G1 by nutrient depletion, irradiated and then subcultured, a subpopulation of cells at the next metaphase contained not only chromosome-type aberrations, but also triradials and chromatid exchanges. The triradials were found to be the result of chromosome-type breaks in three chromosomes, followed by exchange of chromatids. Obviously, chromatid exchanges and dicentrics could arise by the same mechanism. Triradials and chromatid exchanges were not found in cells irradiated in G1 without nutrient depletion. It appears, therefore, that nutrient depletion can affect the capacity of cells to repair X-ray induced damage. The types of aberrations suggest that the lesions which form them cause real physical discontinuities of the chromosomes, with movement of the broken ends before exchange formation.