The effect of cycloheximide on repair in a temperature conditional radiation-sensitive mutant of Saccharomyces cerevisiae.

Previous results [M. Budd and R. K. Mortimer, Mutat. Res. 103, 19-24 (1982)] have shown that rad54-3 strains are temperature conditional for double-strand break repair. At the temperature where survival is high, 23 degrees C, rad54-3 strains are able to repair X-ray-induced double-strand breaks, while at the temperature where survival is low, 36 degrees C, these strains are unable to repair rad54-3 strains provide a system to study the effects of drugs that block protein synthesis such as cycloheximide on repair of X-ray damage. Repair of X-ray damage is studied by irradiating rad54-3 cells, incubating them at the permissive temperature, 23 degrees C, for 5 hr, shifting the cells to the restrictive temperature, 36 degrees C, and assaying for colony-forming ability. Comparing the survival of these cells with those which had been continuously incubated at the restrictive temperature after irradiation shows the extent of repair. Addition of cycloheximide at the time of irradiation causes an inhibition of repair. If cycloheximide is added a short time after irradiation, an enhanced recovery is observed compared with the addition of the drug at the time of irradiation. One explanation for the enhanced recovery is an increased synthesis of repair enzymes after irradiation.