A Comparative Study of the Retardation of Budding and Cellular Inactivation by Ultraviolet Radiation in Polyploid Saccharomyces with Special Reference to Photoreactivation

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1. The curves representing the retardation of budding of ultraviolet in Saccharomyces are sigmoid for diploid, triploid, and tetraploid cells and exponential for haploid cells. When the curves are interpreted in terms of the multi target hypothesis, a one to one correspondence can be shown between the number of chromosome sets and the number of radio-sensitive sites per cell.
2. The rates of logarithmic inhibition of budding increase linearly with increasing polyploidy.
3. The retardation of budding by ultraviolet is photoreversible. However, photorecovery does not proceed in accordance with the dose reduction principle. After photoreactivation, cells of the entire polyploid series yield exponential inhibition of budding curves whose slopes vary independently of the number of chromosome sets per cell.
4. Survival curves for all members of the polyploid series are sigmoid. Target values show a non unitary increase with polyploidy though the rates of logarithmic inactivation are independent of the number of chromosome sets per cell. Inactivation rates are related closely, however, to the slopes of the curves for inhibition of budding which are obtained after photoreactivation.
5. Photoreactivation of inactivated cells obeys the dose reduction principle. The same proportion of damage is repaired per unit of visible light in all cells of the polyploid series.
6. The depression of budding activity by ultraviolet reflects damage scored upon both genetic and non genetic cellular components. The non genetic damage is related closely to the damage effecting cellular inactivation.