UNIQUE DNA-REPAIR PROPERTY OF AN ULTRAVIOLET-SENSITIVE (RADC) MUTANT OF DICTYOSTELIUM-DISCOIDEUM

Dictyostelium discoideum is an organism that shows higher UV resistanc e than other organisms, such as Escherichia coli and human cultured ce lls. We examined the removal of cyclobutane pyrimidine dimers (CPD) an d 6-4 photoproducts from DNA in the radC mutant and the wild-type stra in using an enzyme-linked immunosorbent assay with monoclonal antibodi es. Wild-type cells excised more than 90% of both CPD and 6-4 photopro ducts within 4 h. Dictyostelium discoideum appeared to have a special repair system, because 6-4 photoproducts were repaired faster than CPD in E. coli and human cultured cells. In radC mutant cells, although o nly 50% of CPD were excised from DNA within 8 h, effective removal of 6-4 photoproducts (80% in 8 h) was observed. Excision repair-deficient mutants generally cannot remove both CPD and 6-4 photoproducts. Thoug h the radC mutant shows deficient excision repair, it can remove 6-4 p hotoproducts to a moderate degree. These results suggest that D. disco ideum has two kinds of repair systems, one mainly for CPD and the othe r for 6-4 photoproducts, and that the radC mutant has a defect mainly in the repair enzyme for CPD.