Evidence From Photoreactivation Kinetics for Multiple Dna Photolyases in Yeast

Abstract

Abstract— We have analyzed the kinetics of photoreactivation of ultraviolet‐light‐irradiated cells of two strains of the yeast Saccharomyces cerevisiae. The analysis yields plots of h(t), the number of photorepairable lethal hits remaining in the cell as a function of the time t of exposure to a continuous source of photoreactivating light. In the case of one of the strains studied, an excision‐deficient haploid strain, it is found that the time‐dependence of h(t) is given by the sum of three decreasing exponential functions of t for stationary phase cultures grown at 23 or 30°C. When the culture is grown at 37°C. the fastest component is absent and the intermediate component is reduced in importance relative to the remaining slow component. In the case of the other strain, a diploid of wild‐type radiation resistance, h(t) is found to contain just one decreasing exponential for cultures grown at 23, 30, and 37°C. The rate constant depends on the growth temperature of the cells, decreasing with increasing temperature. The results are interpreted as evidence for multiple DNA photolyases in the sensitive haploid strain.

Solvent Dependence of Pyrimidine Dimer Splitting in a Covalently Linked Dimer‐indole System

“…Photolyases from a variety of species have been characterized (Sabourin and Ley, 1988;Eker et al, 1986;Johnson and Haynes, 1986;Sancar et al, 1984). All known photolyases utilize two noncovalently bound cofactors as sensitizers, one of which is the dihydroflavin FADH2 (Wang and Jorns, 1989;Wang et al, 1988;Payne et al, 1987;Eker et al, 1986).…”

Kinetics of Photoreactivation and Liquid‐holding Recovery in Yeast Cells

“…More complicated kinetics may result if multiple repair processes are operating independently with different rates. Such cases are discussed elsewhere (Johnson and Haynes, 1986).…”