Absence of Photoreactivation of Pyrimidine Dimers in the Epidermis of Hairless Mice Following Exposures to Ultraviolet Light*

Abstract—The influence of photoreactivating light on the fate of UV‐induced DNA damage has been measured in the epidermis of hairless mice using damage‐specific endonuclease from Micrococcus luteus . Groups of mice were exposed to varying fluences of UV at 297nm or from an FS40 fluorescent sun lamp to induce UV photoproducts. The same fluence‐dependent DNA damage was observed in high molecular weight epidermal DNA regardless of whether the mice were killed immediately, or maintained in the dark or under photoreactivating light for 20 h after UV. Thus, no detectable photoreactivation of UV‐induced pyrimidine dimers could be demonstrated in mouse epithelial cells in vivo .