ADAPTIVE RESPONSE TO MUTAGENESIS AND ITS MOLECULAR-BASIS IN A HUMAN T-CELL LEUKEMIA LINE PRIMED WITH A LOW-DOSE OF GAMMA-RAYS

The effect was studied of a low dose of gamma-ray preexposure on the f requency and molecular spectrum of radiation-induced mutations at the hprt locus in a human T-cell leukemia line. When the cells were preexp osed to 0.01 Gy of gamma-rays, the yield of mutations induced by a sub sequent 2-Gy challenge dose was reduced by 60%, compared with the 2 Gy of irradiation alone. The data of Southern blot analysis showed that 47% of the mutants induced by 2 Gy in the cells without low-dose preex posure were of the deletion or rearranged mutations type. In contrast, in the low-dose radioadapted cells the proportion of this type of 2-G y-induced mutations decreased to 28%. This is close to the control lev el (22%) of spontaneous mutations. Our results confirm that a low dose of gamma-ray preexposure leads to a decreased susceptibility to gene deletions and rearrangements after high-dose irradiation.