Effect of ionizing radiation and low temperature on L5178Y-R and L5178Y-S cells. I. DNA strand breaks induced by decays of incorporated 3H and 125I.

The induction and repair of DNA strand breaks induced by disintegration of 3H and 125I incorporated into DNA was examined by the DNA unwinding technique in two strains of murine L5178Y lymphoma cells. The L5178Y-S cells are extremely sensitive to decay of 3H incorporated into DNA, L5178Y-R cells have rather 'normal' sensitivity. The number of strand breaks induced during a cold treatment was about 2.2 per 3H decay and 4 per 125I decay. No differences were found between the two strains. During the labelling period accumulation of unrepaired DNA strands occurred. About 80 per cent of all 125I induced DNA strand breaks was left unrepaired after a 21 h labelling period. No differences occurred between the two cell strains. It thus seems that the marked difference between the two cell strains in sensitivity to decay of the nuclides incorporated into DNA is not due to differences in the rejoining capacity of DNA strand breaks.