RPA and ATR link transcriptional stress to p53

The mechanisms by which DNA-damaging agents trigger the induction of the stress response protein p53 are poorly understood but may involve alterations of chromatin structure or blockage of either transcription or replication. Here we show that transcription-blocking agents can induce phosphorylation of the Ser-15 site of p53 in a replication-independent manner. Furthermore, microinjection of anti-RNA polymerase II antibodies into the nuclei of cells showed that blockage of transcription is sufficient for p53 accumulation even in the absence of DNA damage. This induction of p53 occurs by two independent mechanisms. First, accumulation of p53 is linked to diminished nuclear export of mRNA; and second, inhibition specifically of elongating RNA polymerase II complexes results in the phosphorylation of the Ser-15 site of p53 in a replication protein A (RPA)- and ATM and Rad3-related (ATR)-dependent manner. We propose that this transcription-based stress response involving RPA, ATR, and p53 has evolved as a DNA damage-sensing mechanism to safeguard cells against DNA damage-induced mutagenesis

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