RESPONSES OF RADIOSENSITIVE REPAIR-PROFICIENT CELL-LINES TO RESTRICTION ENDONUCLEASES

Radiosensitive mutant mammalian cell lines fall into two categories: ( 1) those exhibiting a deficiency in the rejoining of dsb, e.g. Chinese hamster xrs and XR1, and murine scid cells; and (2) those exhibiting apparently normal rejoining of bulk dsb, e.g. hamster irs mutants and cells from ataxia-telangiectasia individuals. Cells of both types also show hypersensitivity to restriction endonucleases when applied by ce ll poration techniques. These data are reviewed, and new data are pres ented for Pvu II treatment of the radiosensitive dsb repair-proficient Chinese hamster VC4 mutant, which has been reported to have normal ce llular and chromosomal sensitivity to restriction endonucleases and ne utrons. We find that VC4 is hypersensitive to blunt-ended dsb generate d by PvuII. We conclude that the enhanced sensitivity of this and othe r repair-proficient mutants to radiation and restriction endonucleases results from a dsb processing defect leading to abnormal conversion o f dsb into chromosomal aberrations.