Unique DNA repair property of an ultraviolet-sensitive (radC) mutant of Dictyostelium discoideum.

Dictyostelium discoideum is an organism that shows higher UV resistance than other organisms, such as Escherichia coli and human cultured cells. We examined the removal of cyclobutane pyrimidine dimers (CPD) and 6-4 photoproducts from DNA in the radC mutant and the wild-type strain using an enzyme-linked immunosorbent assay with monoclonal antibodies. Wild-type cells excised more than 90% of both CPD and 6-4 photoproducts 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 only 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. Though the radC mutant shows deficient excision repair, it can remove 6-4 photoproducts to a moderate degree. These results suggest that D. discoideum has two kinds of repair systems, one mainly for CPD and the other for 6-4 photoproducts, and that the radC mutant has a defect mainly in the repair enzyme for CPD.