Sensitivity of Synchronized Chinese Hamster Cells to Ultraviolet Light

The age response for lethality of Chinese hamster cells to ultraviolet light shows that they are resistant in G1, sensitive as they move into and through the S phase and resistant again in G2 and mitosis. Survival curves determined at different times in the cycle reveal that mitotic cells are the most resistant fraction, much more resistant than S cells, and more resistant than either G1 or G2 cells. The extent to which the age response is ilfluenced by nucleic acid and protein synthesis was investigated by using inhibitors of these processes. In the presence of inhibitors of DNA or protein synthesis added to G1 cells before exposure, cell survival neither declines to the minimum survival of S cells nor rises subsequently to the resistance of G2 cells. If, before exposure, DNA synthesis is arrested in the middle of S, when survival is at a minimum, the subsequent rise in survival during G2 is not prevented. However when cycloheximide is added before exposure, during the middle of S, this rise is prevented. When actinomycin D, an inhibitor of RNA synthesis is added prior to exposure the age response is affected only slightly. Postirradiation treatment of G1 and mid-S cells with inhibitors of DNA or protein synthesis maintains survival at a level characteristic of the age of the cells