Mutation induction in haploid yeast after split-dose radiation exposure. II. Combination of UV-irradiation and X-rays.
Split-dose protocols can be used to investigate the kinetics of recovery from radiation damage and to elucidate the mechanisms of cell inactivation and mutation induction. In this study, a haploid strain of the yeast, Saccharomyces cerevisiae, wild-type with regard to radiation sensitivity, was irradiated with 254-nm ultraviolet (UV) light and then exposed to X-rays after incubation for 0-6 hr. The cells were incubated either on nutrient medium or salt agar between the treatments. Loss of reproductive ability and mutation to canavanine resistance were measured. When the X-ray exposure immediately followed UV-irradiation, the X-ray survival curves had the same slope irrespective of the pretreatment, while the X-ray mutation induction curves were changed from linear to linear quadratic with increasing UV fluence. Incubations up to about 3 hr on nutrient medium between the treatments led to synergism with respect to cell inactivation and antagonism with respect to mutation, but after 4-6 hr the two treatments acted independently. Incubation on salt agar did not cause any change in the survival curves, but there was a strong suppression of X-ray-induced mutation with increasing UV fluence. On the basis of these results, we suggest that mutation after combined UV and X-ray exposure is affected not only by the induction and suppression of DNA repair processes, but also by radiation-induced modifications of cell-cycle progression and changes in the expression of the mutant phenotype.
Keller
B
B
Strahlenzentrum der Justus-Liebig-Universität, Giessen, Germany. friedo.zoelzer@townshend.cz
Zölzer
F
F
Kiefer
J
J
D018929:Cell Culture Techniques; D002470:Cell Survival / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006238:Haploidy; D009154:Mutation; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000528:radiation effects*; D013997:Time Factors; D014466:Ultraviolet Rays; D014965:X-Rays