The nature of mutants induced by ionising radiation in cultured hamster cells. 1

A large number of thioguanine (TG)-resistant mutants of V79-4 Chinese hamster cells was isolated from untreated cultures and from cultures exposed to γ-rays, α particles or ethyl methanesulphonate (EMS). Selection conditions were chosen to optimise the survival of all types of TG-resistant mutant, and the isolation procedure ensured that each mutant originated independently of any other. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) enzyme activity was measured in cell-free extracts of each mutant, and compared with repeat measurements made on the parental V79-4 cells and on a series of non-mutant clones. Ionising radiation-induced mutants were found to be mostly (or perhaps entirely) of the 'zero HGPRT activity' type, but about 20% of EMS-induced mutants and 50% of spontaneously occurring mutants had significant HGPRT activity. (orig.)