New roles for DNA topoisomerase I

DNA topoisomerase I is an nuclear enzyme involved in multiple DNA transactions such as replication, transcription and chromosome condensation. Besides its activity of DNA relaxation, that is essential for the removal of torsional constraints associated with these processes, topoisomerase I may have other functions related to its kinase activity, its similarity with DNA recombinases, and its ability to be trapped by various DNA modifications. In this review, recent findings on the poisoning of topoisomerase I by a broad range of DNA lesions are discussed in the context of a possible role of the enzyme in DNA damage signalling to the cell death machinery.