Repair of UV-induced (6-4) photoproducts in nucleosome core DNA.
Using radioimmunoassays, we examined rates of removal of UV-induced pyrimidine-pyrimidone (6-4) photoproducts ((6-4)PDs) and cyclobutane pyrimidine dimers (CPDs) from 146-base pair nucleosome core DNA (and 166-base pair chromatosome DNA) of confluent human diploid fibroblasts. Dose-response experiments indicate that the yield of (6-4)PDs in core DNA is about 30% that of CPDs in the UV dose range of 0-200 J/m2. Repair experiments indicate that, at 40 J/m2, (6-4)PDs are removed much faster (approximately 75% in 2 h) from nucleosome core (and chromatosome) DNA than CPDs (10-15% in 2 h). A slow rate of removal of CPDs is also observed when the UV dose is reduced to 10 J/m2 (i.e. even when the level of CPDs is less than that of (6-4)PDs at 40 J/m2). These results indicate that (a) the accessibility of repair proteins to (6-4)PDs in nucleosomes is markedly different than their accessibility to CPDs and/or (b) repair enzymes are much more efficient at incising and removing (6-4)PDs than CPDs in human chromatin.
Suquet
C
C
Department of Biochemistry and Biophysics, Washington State University, Pullman 99164-4660, USA.
Mitchell
D L
DL
Smerdon
M J
MJ
D002478:Cells, Cultured; D004247:DNA / Q000528:radiation effects*; D004260:DNA Repair; D006801:Humans; D009707:Nucleosomes / Q000378:metabolism*; D011740:Pyrimidine Dimers / Q000378:metabolism*; D014466:Ultraviolet Rays
D009707:Nucleosomes; D011740:Pyrimidine Dimers; C058406:pyrimidine-pyrimidone dimer; D004247:DNA