title: Increased efficiency of photoreversal of UV-induced dimers in the DNA of chick embryo fibroblasts with post-UV dark time.
abstract: The kinetics of photoreversal of UV-induced dimers in the DNA of early passage chick embryo fibroblasts was studied by monitoring disappearance of UV-endonuclease-sensitive sites. Photorepair was found to increase in efficiency when cells were incubated in the dark for several hours at 37 degrees C following the dimer-inducing short-wavelength (254 nm) UV treatment, but prior to the photoreactivating black light (365 nm). Following a UV dose of 10 J/m2 it took at least 4 h in the dark to saturate this effect. This UV dose inserts roughly 2.4 dimers/10(7) daltons of DNA. Dark repair removes about 0.08 dimers/h/10(7) daltons. After 6 h in the dark, exposure to black light removes an additional 1.4 dimers/10(7) daltons leaving about 0.5 dimers unaffected by this treatment. After saturation of the dark effect, the amount of photoreactivation depends only on total black light fluence and not on fluence rate for the range of rates studied. This indicates that during 30 min, the maximum time of black light exposure, no appreciable reattachment of the photorepair molecule to additional unrepaired dimer sites occurs. We estimate that the number of effective photorepair molecules per chick chick cell is at least of the order of 2 x 10(5).
mesh_terms: D000818:Animals; D002460:Cell Line; D002642:Chick Embryo; D004247:DNA / Q000528:radiation effects; D004260:DNA Repair / Q000528:radiation effects*; D003624:Darkness; D011740:Pyrimidine Dimers / Q000528:radiation effects*; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D011740:Pyrimidine Dimers; D004247:DNA