Nucleotide Excision Repair in Human Cells: FATE OF THE EXCISED OLIGONUCLEOTIDE CARRYING DNA DAMAGE IN VIVO

Nucleotide excision repair is the sole mechanism for removing the major UV photoproducts from genomic DNA in human cells. In vitro with human cell-free extract or purified excision repair factors, the damage is removed from naked DNA or nucleosomes in the form of 24- to 32-nucleotide-long oligomers (nominal 30-mer) by dual incisions. Whether the DNA damage is removed from chromatin in vivo in a similar manner and what the fate of the excised oligomer was has not been known previously. Here, we demonstrate that dual incisions occur in vivo identical to the in vitro reaction. Further, we show that transcription-coupled repair, which operates in the absence of the XPC protein, also generates the nominal 30-mer in UV-irradiated XP-C mutant cells. Finally, we report that the excised 30-mer is released from the chromatin in complex with the repair factors TFIIH and XPG. Taken together, our results show the congruence of in vivo and in vitro data on nucleotide excision repair in humans.Background: Human excision repair removes UV photoproducts in 30-mers in vitro, but this has not been previously observed in vivo.Results: UV photoproducts are removed in vivo as 30-mers in complex with TFIIH both in general repair and in transcription-coupled repair.Conclusion: Primary products of excision repair have been isolated in vivo for the first time.Significance: The study provides novel insights into post-excision steps of human DNA repair.