Diploid yeast cells of different cell ages were compared with respect to their X-ray sensitivity upon immediate plating (IP) and after liquid holding (LH) treatment in the presence and absence of caffeine. Response following IP can be divided into "sensitive" and "resistant" periods each occupying 50% of the cell cycle. The sensitive period includes postbudding, mother-daughter cell separation and early interdivisional cells. Resistance begins in later interdivisional cells and maximizes during early budding. LH obliterates the differences seen with IP. The more sensitive the cell is upon IP, the more it responds to LH, with the result that all cells show the same survival which is essentially that of the most resistant budding cell upon IP. Caffeine, though without effect upon IP survival, reduces the LH survival of all cells to the IP level of prebudding interdivisional cells. These findings are interpreted as resulting from the regulated oscillation during the cell cycle of at least two repair pathways, both of which can also be evoked by LH.

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