Synergistic interaction between UV and ionizing radiation in wild-type Schizosaccharomyces pombe.

A synergistic effect of combined UV and gamma-ray exposure was observed for inactivation of wild-type Schizosaccharomyces pombe. A recombinational repair process, known to be important in restitution of damage induced by both radiations, appears to be involved; a radiation-sensitive mutant defective in this repair pathway showed essentially no synergistic interaction between UV and gamma-rays. Recovery from the synergistic effect of pre-exposure in wild-type cells did not display the expected fast gamma-recovery and slow UV-recovery kinetics previously observed for regain of resistance to further exposure to the same radiation. Rather, UV-irradiated cells recovered quickly from synergistic inactivation on subsequent gamma-exposure, while gamma-irradiated cells recovered UV-resistance slowly. Recovery from synergism thus appears to reflect the nature of the second, and not the initial, radiation.