COMPARISON BETWEEN THE ALKALINE UNWINDING TECHNIQUE AND NEUTRAL FILTER ELUTION USING CHO, V79 AND EAT CELLS

Induction and repair of DNA strand breaks were measured in X-irradiate d CHO, V79 and EAT cells using either the alkaline unwinding or the ne utral filter elution techniques. After irradiation on ice, the cells w ere incubated at 37 degrees C for various times to allow for repair. T he repair curves obtained were quite similar and the fast initial decl ine was always characterized by a half-time of 6-8 min and the final s low phase by a half-time of about 200 min independently of the techniq ue used. The curves were found to differ only in the relative fraction of damage repaired during the fast or slow phase. From the similarity of the half-times it is concluded that the fast phase recorded by alk aline unwinding reflects the repair of single-strand breaks but also t he repair of fast rejoining double-strand breaks. Comparing the known ratio of induced single- and double-strand breaks with the measured ra tio of fast and slowly rejoining strand breaks as derived from the kin etics, it can be further concluded that the slow phase measured by alk aline unwinding covers the repair of both slowly rejoining double stra nd breaks as well as slowly rejoining single strand lesions.