MULTI-SITE DAMAGE AND X-RAY-INDUCED LETHALITY IN YEAST

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Abstract
Lethality Induced by X-rays In yeast probably frequently requires the destruction of several Intracellular sites. The relationship between Induced mltotlc delay and the manner in which lethality Is expressed was studied. The Interval between Irradiation and 1st post-irradiation cell division varied for different manifestations of death. The mltotlc delay Increased In the order cells which survived only 1 or 2 divisions, cells in which lethal damage was sufficiently latent to allow production of abortive colonies, cells which produced sectored colonies, and cells which showed no lethal effects. This positive correlation between induced mitotic delay and ability of cells to maintain post-irradiatton cell division was Interpreted as an indication that repair mechanisms influence the way in which death is manifested. The data suggested that differences In ability to maintain post-irradiation cell division reflect quantitative differences In extent of sustained damage, i.e. in number of affected sites. Mitotic delay increases the probability that all affected sites will be repaired, but partial repair (repair at a fraction of affected sites) only convertes lethal damage of more immediate expression to that of less immediate expression. There was no evidence of repair of lethal damage after the 1st post-irradiation cell division; greater mitotic delay in the interval between 1st and 2nd divisions was accompanied by reduced ability to maintain further cell divisions.