Stress-inducible DNA repair in Saccharomyces cerevisiae.

Saccharomyces cerevisiae shows altered radiation response under various stress conditions, such as nutrition depletion, nitrogen starvation, osmotic shock, heat shock, and mild chemical treatments. In general, the cells show higher levels of UV or gamma radiation resistance under the stress. However, not all the stress conditions affect the repair system in the same manner. For example, depletion of nitrogen supply in the growth medium has been shown to enhance the repair of gamma ray-induced DNA damage without significantly affecting the UV response of the cells. On the other hand, a mild treatment with alkali or hydrogen peroxide improves the response to UV light but not to gamma radiation. It has further been shown that the effect of these stresses are not additive, e.g., the alkali and hydrogen peroxide treatments given simultaneously show the same effect as either of them alone. Low levels of gamma and UV radiation exposures are also treated as stress in the present context. Studies show that irradiation of low-dose gamma rays results in enhanced excision repair of UV-induced pyrimidine dimers. However, in all the wild-type strains tested, none showed any effect on gamma rays response. The exposure to low doses of UV light did not show any effect on either the gamma rays or the UV response. It is suggested that the stress-induced enhancement of DNA repair can be of two types: 1) A general response to stress, which prepares the organism to survive in adverse circumstances (some of the proteins produced during this response also take part in the DNA repair), and 2) a particular response involving DNA damage, such as that caused by gamma irradiation. In this case, the DNA damage may act as a signal for enhancement of the DNA repair.