Tanning as part of the eukaryotic SOS response

We have determined that DNA damage is at least one of the signals generated by ultraviolet radiation that stimulates pigmentation (tanning) in human s kin. This photoprotective response is functionally similar to the SOS respo nse described in bacteria. Here we present evidence that DNA damage stimula tes pigmentation, at least in part, through up-regulation of tyrosinase mRN A and protein levels. Furthermore, this response can be induced in the abse nce of DNA damage by treatment of melanocytic cells and intact sl;in with s mall DNA fragments, particularly thymidine dinucleotides, pTpT, Topical app lication of these DNA fragments should provide a photoprotective tan to hum an skin without the harmful effects of ultraviolet radiation.