Evidence to support the existence of efficient DNA double-strand bread rejoining in a radiosensitive mutant of V79-4 following irradiation with 250 kVp x-rays or neutrons

The repair of ionising-radiation-induced DNA double-strand break type damage was measured by Kohn neutral elution in an X-ray-sensitive mutant of V79-4, irs1. This was done in order to investigate further the likelihood that irs1 carries a defect which leads to error-prone repair of DNA damage. The mutant displayed an equal increase in sensitivity to the lethal effects of neutrons, as compared to X-rays. The induction of DNA double-strand breaks was measured in both cell lines. Induction of breaks by X-rays in irs1 seemed to increase slightly with dose, relative to induction in V79-4. Neutron irradiation resulted in a more similar level of induction in either strain after 10-40 Gy. This difference in induction of damage may be due to a different cell-cycle composition in either cell line. The rejoining of X-ray induced double-strand breaks showed a very similar pattern in both cell lines. Neutron-induced breaks, however, were rejoined more efficiently in irs1 again on a percentage basis, but also in absolute terms since similar induction was seen after 40 Gy. This data, together with the differences seen in the rejoining of X-ray compared to neutron induced breaks, may indirectly support the proposal that irs1 is a misrepair mutant. (author). 19 refs.; 6 figs