DNA topoisomerase I and repair of genomic damage

Recent evidence indicates that unrepaired genomic damage influences the catalytic activities of DNA topoisomerases. DNA lesions such as base mismatches, pyrimidinic dimers, 6,4-pholoproducts, apurinic and apyrimidinic sites and others, enhance topoisomerase I mediated DNA cleavage. These findings suggest that topoisomerase activity can be influenced by spontaneous, as well as environmentally induced damages to DNA. In this study the catalytic activity of topoisomerase I was examined in Xeroderma pigmentosum cell lines B and C and compared with the activity of normal human cells. The data show that topoisomerase I levels are higher in two repair-deficient cell lines. This provide novel insight into the mechanism of action of topoisomerases and raise new questions regarding mechanism of topoisomerase-targeting drugs.