Synchronous cultures of early G1 cells were exposed to UV and their ability to photoreactivate lethal and aberrational damage was determined as a function of time following UV exposure. Lesions leading to cell death were converted to a non-photoreactivable state before cells entered S phase, while lesions leading to chromosomal aberrations were converted to a non-photoreactivable state as the cells entered S phase. These results indicate that the intracellular mechanism which expresses photoreactivable UV-induced lesions in G1 cells as cell death is not identical to the mechanism which expresses such lesions as chromosomal aberrations, and the two mechanisms operate primarily in different phases of the cell cycle.

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