Fluence rate as a determinant of synergistic interaction under simultaneous action of UV light and mild heat in Saccharomyces cerevisiae.

In experiments with wild-type diploid yeast cells of Saccharomyces cerevisiae, the synergistic lethal action of a simultaneous application of ultraviolet (UV) light (wavelength, 254 nm) and mild heat (45-57.5 degrees C) was studied. It was shown that, at any fixed UV light intensity, the synergistic effect occurred within the given temperature interval. The optimal temperature to achieve the greatest synergistic effect may be shown for every fluence rate examined. The correlation between the optimal temperature that maximized the synergy and UV light intensity was estimated: this temperature shifted towards higher temperature values with an increasing fluence rate. A possible interpretation of this effect is based on the supposition that the mechanism of the synergistic effect is related to additional lethal damage produced by the interaction of sublesions induced by each agent. These sublesions are supposed to be non-lethal when each agent is applied separately.