Determination of radiation equivalence of ethyl methanesulphonate (EMS) for induction of gene conversion in diploid yeast.

A unit Rad-Equivalent Chemical (REC) has been suggested for purposes of quantitating the mutagenic hazards of chemicals. The usefulness of this approach is demonstrated by the establishment of a constant relationship between the forward mutation frequency and haploid genome size in various organisms for both radiation and chemical EMS. However, it is necessary to determine the radiation equivalence of chemicals in as many organisms and for as many end-points as possible. For end-points we are limited to forward mutations. Another relevant genetic end-point of interest in this regard is gene conversion which can also monitor any kind of DNA damage in a suitable diploid system. Hence, we have determined the REC value for EMS in diploid yeast with gene conversion as the end-point. This agrees well with the REC values estimated in a number of organisms with forward mutation as the end-point. This finding further underlines the generality of the REC concept.