Suquet C, Mitchell D L, Smerdon M J
Department of Biochemistry and Biophysics, Washington State University, Pullman 99164-4660, USA.
J Biol Chem. 1995 Jul 14;270(28):16507-9. doi: 10.1074/jbc.270.28.16507.
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.
我们使用放射免疫分析法，检测了汇合的人二倍体成纤维细胞核小体核心DNA（以及166碱基对的染色质体DNA）中紫外线诱导的嘧啶 - 嘧啶酮（6 - 4）光产物（（6 - 4）PDs）和环丁烷嘧啶二聚体（CPDs）的去除率。剂量反应实验表明，在0 - 200 J/m²的紫外线剂量范围内，核心DNA中（6 - 4）PDs的产量约为CPDs的30%。修复实验表明，在40 J/m²时，（6 - 4）PDs从核小体核心（和染色质体）DNA中的去除速度比CPDs快得多（2小时内约75%）（2小时内为10 - 15%）。当紫外线剂量降至10 J/m²时（即即使CPDs的水平低于40 J/m²时（6 - 4）PDs的水平），也观察到CPDs的去除速度较慢。这些结果表明：（a）修复蛋白对核小体中（6 - 4）PDs的可及性与它们对CPDs的可及性明显不同，和/或（b）在人类染色质中，修复酶切割和去除（6 - 4）PDs比CPDs的效率要高得多。
