INCREASED SENSITIVITY TO KILLING BY RESTRICTION ENZYMES IN THE XR-1 DNA DOUBLE-STRAND BREAK REPAIR-DEFICIENT MUTANT

Repair or misrepair of DNA double-strand breaks (DSBs) is critical in determining cellular survival after γ-irradation. In this report, wer focus on the cellular and biochemical consequences of restriction enzyme induced DSBs in wild-type Chinese hamster ovary (CHP) cells and the DNA DSB repair-defective mutant XR-1. We find that XR-1 possess reduced cellular survival after the induction of restriction enzymes that produce either cohesive or blunt ends. XT-1's sensitivity to killing by restriction enzymes strongly mimics to its response to γ-rays. Using pulsed field electrophoresis, we find that for each enzyme, similar numbers of DNA DSBs are being intorduced in both cell lines. The simplest explanation for the increased sensitivity to restriction enzymes in the mutant is that the biochemical defect in XR-1 is not confined to the repair of ionizing radiation induced ends, but extends to DSBs that possess ligatable 3′-hydroxyl and 5′-phosphate ends as well. © 1990.