Similar responses to ionizing radiation of fungal and vertebrate cells and the importance of DNA double-strand breaks

The sensitivity to ionizing radiation has been examined in several fungi and vertebrate cell lines by determining the relative number of lesions required to kill to 10% survival (LD10 X DNA content). Although the DNA content varied by over 1000 times, the (LD10 X DNA) for the different organisms including different ploidies of the same organism varied by less than a factor of 10 so long as the cells were at least diploid or were haploids in the G-2 phase of the cell cycle. Haploid cells that were in the G-1 stage were generally very sensitive. The data are consistent with the idea that there may be similar mechanisms of repair requiring duplicated chromosomes and that unrepaired DNA double-strand breaks are generally lethal. (author)