Coordination of dual incision and repair synthesis in human nucleotide excision repair

Nucleotide excision repair (NER) requires the coordinated sequential assembly and actions of the involved proteins at sites of DNA damage. Following damage recognition, dual incision 50 to the lesion by ERCC1-XPF and 30 to the lesion by XPG leads to the removal of a lesion-containing oligonucleotide of about 30 nucleotides. The resulting single-stranded DNA (ssDNA) gap on the undamaged strand is filled in by DNA repair synthesis. Here, we have asked how dual incision and repair synthesis are coordinated in human cells to avoid the exposure of potentially harmful ssDNA intermediates. Using catalytically inactive mutants of ERCC1-XPF and XPG, we show that the 50 incision by ERCC1-XPF precedes the 30 incision by XPG and that the initiation of repair synthesis does not require the catalytic activity of XPG. We propose that a defined order of dual incision and repair synthesis exists in human cells in the form of a 'cut-patch-cut-patch' mechanism. This mechanism may aid the smooth progression through the NER pathway and contribute to genome integrity

Understanding nucleotide excision repair and its roles in cancer and ageing

Nucleotide excision repair (NER) eliminates various structurally unrelated DNA lesions by a multiwise 'cut and patch'-type reaction. The global genome NER (GG-NER) subpathway prevents mutagenesis by probing the genome for helix-distorting lesions, whereas transcription-coupled NER (TC-NER) removes transcription-blocking lesions to permit unperturbed gene expression, thereby preventing cell death. Consequently, defects in GG-NER result in cancer predisposition, whereas defects in TC-NER cause a variety of diseases ranging from ultraviolet radiation-sensitive syndrome to severe premature ageing conditions such as Cockayne syndrome. Recent studies have uncovered new aspects of DNA-damage detection by NER, how NER is regulated by extensive post-translational modifications, and the dynamic chromatin interactions that control its efficiency. Based on these findings, a mechanistic model is proposed that explains the complex genotype-phenotype correlations of transcription-coupled repair disorders

Control of structure-specific endonucleases to maintain genome stability

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