Ionizing radiation damage repair:: a role for topoisomerases?

In parallel with the developing field of DNA topoisomerase poisons in tumor chemotherapy, the basic features of these nuclear enzymes have been unfolded. The role of topoisomerases in fundamental processes involving DNA metabolism has been shown to outpace by far the initial expectations. While DNA topoisomerases are involved in relaxation of chromatin to relieve tension during DNA replication and transcription, as well as for recombinational processes and chromosome segregation and condensation, the possible role, either direct or indirect, of these enzymes in DNA repair is still a matter of discussion. In this survey the possible relationship of topoisomerases with the repair of ionizing radiation damage in mammalian cells is considered, on the basis of attractive 'clues' and in the light of a number of observations.