IS RADIATION-GENERATED AQUEOUS ELECTRON-TYPE DAMAGE REPAIRED BY THE RECOMBINATIONAL REPAIR PATHWAY IN SACCHAROMYCES-CEREVISIAE

The lethal effects of .gamma.-radiation-induced aqueous electron[e.hivin.aq]-type damage were compared to hydroxyl radical-type damage in S. cerevisiae by irradiation in the presence of N2 or N2O, and the influence of cellular excision and recombinational repair capacity has been assessed. N2O can scavenge e.hivin.aq and convert them to OH.cntdot.. Recombination-proficient diploid cells showed increased sensitivity to irradiation in the presence of N2O compared to N2, suggesting that damage of the OH.cntdot. type is more serious than that of the e.hivin.aq-type in these cells. Excision-defective diploid cells responded in the same manner as wild-type or other rec+ diploids. Recombination-deficient diploid or haploid cells, however, showed no increase in lethality when irradiated in the presence of N2O, suggesting that the 2 types of damage are about equivalent in rec- strains. Haploid rec+ cells showed no difference in sensitivity to irradiation in N2 compared to N2O when the cells were in G1 phase, where they contain only one gene copy and where recombination is therefore not possible, but showed a large increase in sensitivity in N2O when they were in G2 phase. Apparently e.hivin.aq-type damage can be lethal. It is, however, apparently repaired in rec+ strains, and with an efficiency greater than that for OH.cntdot. type damage.