Evidence for an indirect effect of radiation on mammalian chromosomes. II. UV-induced isochromosome formation in cell hybrids.

Cell fusion has been used to test the hypothesis that chromosomes may be damaged indirectly by UV light, as well as by direct interaction with DNA. Hybrids were found to contain isochromosomes of mouse origin, whose frequency increased as the dose of UV delivered to the hamster cell parent was increased. This unusual type of aberration was shown to be induced also by direct UV irradiation of mouse or hybrid cells. These results suggest that UV light has a hitherto undiscovered indirect effect on chromosome integrity, mediated by some irradiated cell component.