DNA repair in a UV-sensitive mutant of a mouse cell line

A UV-sensitive mutant, Q31, isolated from mouse-lymphoma L5178Y cells, was studied for excision and post-replication repairs. A nearly equal number of UV endonuclease-sensitive sites was induced by UV in L5178Y, Q31, and human Raji cells. L5178Y cells irradiated with 10 J/m2 removed 18% of sensitive sites from DNA of detection, whereas Raji cells eliminated about 60% of the sites. These results during incubation for 24 h, and Q31 cells removed 3% of the sites, a fraction less than the limit indicate that mouse-lymphoma cells are capable of excision repair to a limited extend as compared with human cells and that mutant Q31 cells are essentially devoid of dimer excision. The newly synthesized DNA was of smaller size in UV-irradiated and unirradiated Q31 cells than that in the corresponding L5178Y cells, but the DNAs in both cell strains increased to comparable sizes after a 2-h chase.