An Investigation of (a) Variation in Rate of DNA-synthesis During S-phase in Mouse L-cells (b) Effect of Ultra-violet Radiation on rate of DNA-synthesis

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Abstract
Mouse L-strain cells were grown in tissue culture and used for experiments when they were in the exponential phase of growth. Both autoradiographic measurements of the rate of DNA-synthesis and microspectrophotometric measurements of the total DNA-content were made on individual cells (a) in normal cultures, (b) in cultures which had been irradiated with ultra-violet light, (c) in cultures in which some of the cells had received a microbeam dose of ultra-violet radiation into an area of the nucleus approximately 3 µ in diameter. From the results, it was first possible to establish the relative lengths of the G1, S and G2 phases of the mitotic cycle for this type of cell. A more detailed analysis of the results showed how the rate of DNA-synthesis varies through the S-phase, and the irradiation experiments indicated that when the rate of DNA-synthesis is used as a criterion of sensitivity, the sensitivity of the cells to ultra-violet irradiation increases steadily during the synthetic phase.