Effect of chemical protectors on fast-neutron-induced reversions in yeast

A diploid strain of yeast, Saccharomyces cerevisiae, was used and arginine reversions were assayed by plating the cells on plates (Arg-) of synthetic medium containing all amino acids except arginine. Reversions were expressed in relation to the number of surviving cells, and it was found that the neutron doses were low enough to give 100% survival for the largest exposure (420 rad). A correction was made for the measured γ contamination of the neutron dose-rate, and plots of net reversion frequency against neutron dose demonstrated a positive protection against neutrons by the chemicals dimethyl sulphoxide (DMSO, 10% V/V), thiourea (TU, 1 mM) and methanol (1 mM). The dose-modifying factor was 1.45. This protection is attributed to .OH radical scavenging by the chemicals. (U.K.)