Differences in removal of acetylaminofluorene and pyrimidine dimers from the DNA of cultured mammalian cells

The rate and extent of disappearance of 2 DNA lesions (pyrimidine dimers and covalently bound acetylaminofluorene), both thought to be removed by the socalled wide patch (approximately 100 nucleotides) repair process, were studied in a variety of cultured mammalian cells. With the exception of mouse cells, dimers were removed more rapidly and extensively than covalently bound acetylaminofluorene. In human cells, for example, about 50% of the dimers were excised from DNA in 1 hr while only 25 to 50% of the chemically induced lesions were excised from DNA after 48 hr. Surprisingly mouse cells, which remove few dimers, were about as competent as control human fibroblasts at removing acetylaminofluorene lesions; however, xeroderma pigmentosum cells (group D) removed fewer N acetoxy 2 acetylaminofluorene induced lesions than control human cells. The data raise the possibility of separate repair processes for these 2 types of lesions and suggest that their expression may be under similar genetic control in human cells.