A number of radiation sensitive mutants of yeast were examined for their sensitivity to the inactivating agents, ultraviolet light (UV), gamma irradiation, ethyl methane sulphonate (EMS) and heat treatment (52° and 37°).
A mutant of the gene rad-3, isolated on the basis of its primary sensitivity to UV showed sensitivity only to UV. In contrast the five X-ray sensitive mutants were sensitive to all four inactivating treatments. Considerable variation was observed in the response of the mutants to liquid holding treatment in non-nutrient solution.
The data concerning the heat sensitivity of the X-ray sensitive mutants confirms the correlation between heat and X-ray sensitivity observed in bacteria by Bridges (1969).
The results indicate that at least two separable pathways of cellular repair exist in yeast, one effective in the repair of UV damage and the other effective in the repair of ionising radiation, alkylating agents, heat and a fraction of UV damage.
Communicated by F. Kaudewitz