DNA strand break and rejoining in cultured human fibroblasts exposed to fast neutrons or gamma rays

The production and rejoining of DNA single-strand and double-strand breaks have been monitored in monolayer cultures of proliferating human skin fibroblasts. The yield of single-strand breaks induced by neutrons was 30 per cent of that produced by the same dose of #betta#-rays; whilst in the induction of double-strand breaks neutrons were 1.6 times as effective as #betta#-rays. Upon post-irradiation incubation of cells at 370C, neutron-induced single-strand and double-strand breaks were rejoined with a similar time-course to #betta#-induced breaks. Rejoining followed biphasic kinetics; of the single-strand breaks, 50 per cent disappeared within 2 min after #betta#-rays and 6-10 min after neutrons. Fifty per cent of the double-strand breaks disappeared within 10 min, after #betta#-rays and neutrons. (author)