Suspension cultures of mouse L cells were irradiated with ultraviolet light at exposures of 40, 100, and <tex-math>$200\ {\rm ergs}/{\rm mm}^{2}$</tex-math>, which reduced the colony-forming ability of asynchronous cell populations to 95%, 70%, and 20% of the control value. The rate of DNA synthesis in irradiated cells was found to be temporarily depressed, but initiation of DNA synthesis as measured by entry of G1 phase cells to S phase was not inhibited. Cell populations irradiated in G1 or G2 phase showed no delay in their movement to S phase or to mitosis, respectively, but cell populations irridiated in S phase had a delay in their progression to G2 phase. Quantitative measurements showed that cell populations irradiated in late G1 or early S phase had a longer delay and a larger fraction of cells which failed to reach mitosis than cells irradiated in late S phase. The fraction of cells which failed to reach mitosis after irradiation was equal to the fraction of cells which lost their colony-forming ability, indicating that whether a cell would survive or not was determined in its first generation after UV irradiation.

This content is only available as a PDF.
You do not currently have access to this content.