LOSS OF PHOTOREVERSIBILITY OF SUNBURN CELL INDUCTION IN Monodelphis domestica

Exposure of the South American opossum, Monodelphis domestica, to ultraviolet radiation (UVR) resulted in the formation of sunburn cells (SBCs) in the epidermis. If, however, the UVR was immediately followed by an exposure to photoreactivating light, which reversed ∼ 95% of the UVR‐induced pyrrolidine dimers in epidermal DNA, the appearance of SBCs was suppressed by ∼ 90%. Delaying the photoreactivation (PR) treatment resulted in a progressive loss with time in the capacity of the PR treatment to suppress SBC induction. PR treatment administered 12 h after UVR exposure resulted in only an ∼ 11% suppression of SBC formation even though ∼ 97% of the remaining pyrimidine dimers were repaired by the PR exposure.