Conconi Antonio, Paquette Michel, Fahy Deirdre, Bespalov Vyacheslav A, Smerdon Michael J
Département de Microbiologie et d'Infectiologie, Faculté de Médecine, Poste 7446, Université de Sherbrooke, 3001 12th Ave. Nord, Sherbrooke, QC J1H 5N4, Canada.
Mol Cell Biol. 2005 Nov;25(22):9773-83. doi: 10.1128/MCB.25.22.9773-9783.2005.
Chromatin rearrangements occur during repair of cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair (NER). Thereafter, the original structure must be restored to retain normal genomic functions. How NER proceeds through nonnucleosomal chromatin and how open chromatin is reestablished after repair are unknown. We analyzed NER in ribosomal genes (rDNA), which are present in multiple copies but only a fraction are actively transcribed and nonnucleosomal. We show that removal of CPDs is fast in the active rDNA and that chromatin reorganization occurs during NER. Furthermore, chromatin assembles on nonnucleosomal rDNA during the early events of NER but in the absence of DNA repair. The resumption of transcription after removal of CPDs correlates with the reappearance of nonnucleosomal chromatin. To date, only the passage of replication machinery was thought to package ribosomal genes in nucleosomes. In this report, we show that early events after formation of UV photoproducts in DNA also promote chromatin assembly.
在通过核苷酸切除修复（NER）修复环丁烷嘧啶二聚体（CPD）的过程中会发生染色质重排。此后，必须恢复原始结构以保留正常的基因组功能。NER如何穿过非核小体染色质以及修复后如何重新建立开放染色质尚不清楚。我们分析了核糖体基因（rDNA）中的NER，rDNA有多个拷贝，但只有一小部分是活跃转录的且是非核小体的。我们发现，在活跃的rDNA中CPD的去除很快，并且在NER过程中会发生染色质重组。此外，在NER的早期事件中，染色质会在非核小体rDNA上组装，但此时不存在DNA修复。CPD去除后转录的恢复与非核小体染色质的重新出现相关。迄今为止，人们认为只有复制机制的通过才能将核糖体基因包装在核小体中。在本报告中，我们表明DNA中紫外线光产物形成后的早期事件也会促进染色质组装。
