Diploidy and repair of radiation damage in Saccharomyces mutants

Contribution of a photoreactivable component to the oxygen effect observed in certain rad mutants of Saccharomyces cerevisiae after exposure to high energy electrons

It is shown that a fraction of damage induced by high energy electrons (25 MeV) in certain rad mutants of the yeast Saccharomyces cerevisiae can be photoreactivated. The photoreactivable damage contributes to the lethal effect of this type of irradiation and modifies the oxygen effect. Using photoreactivating light or nigrosin, the amount of photoreactivable damage is reduced and the oxygen enhancement ratio (OER) for yeast mutants increases approximately to the OER found in wild-type cells.

Reduced PLD repair ability in glutathione synthetase deficient human fibroblasts after UV irradiation

Using a human cell strain deficient in glutathione synthetase and a related control, the role of glutathione in repair mechanisms has been investigated. UV light has been used in order to avoid the interaction between thiols and free radicals. When potentially lethal damage repair is completed, deficient cells in plateau phase exhibit smaller surviving fractions than do control cells. The ratio of surviving fractions in control/deficient cells is about 2 for the same radiation dose. These results indicate that thiols and especially GSH are involved in repair mechanisms.

The oxygen effect in haploid and diploid yeast strains of different sensitivities

The extent of the oxygen effect for cell survival was studied in diploid and haploid wild-type yeast and in mutants belonging to the rad2, rad6 and rad50 epistatic group. In haploids, reduced oxygen enhancement ratios were found in rad52, rad6 and rad18. The latter two also showed some influence of the mating type. In diploids the oxygen effect was decreased in rad2, rad52 and rad18.

Modification of high LET radiation-induced damage and its repair in yeast by hypoxia

The lethal response of a diploid yeast strain BZ34 to densely ionizing radiations from the reaction 10B(n, alpha)7 Li was studied. The values for relative biological effectiveness (r.b.e.) and oxygen enhancement ratio (o.e.r.) for this radiation compare favourably with the data obtained with charged particles on the same strain of yeast. Recovery from potentially lethal damage was also studied by post-irradiation holding under non-nutrient conditions. In order to understand the role of oxygen in the recovery process, the investigation covered the following treatment regimens: (a) aerobic irradiation and aerobic holding (A-A), (b) aerobic irradiation and hypoxic holding (A-H), (c) hypoxic irradiation and hypoxic holding (H-H) and (d) hypoxic irradiation and aerobic holding (H-A). It has been found that the presence of oxygen is essential for recovery from the damage induced by both gamma rays and high linear energy transfer (LET) radiations. The extent of recovery was larger for gamma-induced damage than for damage induced by high LET radiation (alpha + 7Li) for the A-A condition. In the H-H condition, while only a slight recovery was seen for gamma-induced damage, it was totally absent for high LET damage. For the modality A-H, it was found that there is not recovery from the sparsely ionising gamma radiation-induced damage. The implications of these results for the treatment of malignant tumours by radiotherapy are briefly discussed.