Different rate-limiting steps in excision repair of ultraviolet- and N-acetoxy-2-acetylaminofluorene-damaged DNA in normal human fibroblasts.

Abstract

In normal human [fibroblast Rid Mor CRL 1220] cells the amount of excision of UV damage to DNA saturates at high doses. In these cells from chemicals mimic UV damage as far as their biological and repair characteristics are concerned. One of these chemicals is N-acetoxy-2-acetylaminofluorene. The limited repair capacity for UV damage was determined. The effect of treatment with N-acetoxy-2-acetylaminofluorene on the limited repair capacity for UV damage was determined. To measure repair unscheduled DNA synthesis and the number of sites sensitive to an UV endonuclease were determined in an assay using an extract of Micrococcus luteus. The nuclease does not act on DNA treated with the chemical. The amount of unscheduled DNA synthesis due to a combined chemical and UV treatment was the sum of those observed from the separate treatments, even at saturation doses. The combined treatment did not affect the removal of nuclease-sensitive sites. There are probably different rate-limiting steps in excision repair of the UV and the chemical damage. A model involving a complex of enzymes to explain the data is suggested.