[Biological function of DNA topoisomerases and its implication in cancer chemotherapy]

It has been generally recognized that in a variety of biological systems the structural changes such as circularization, looping and supercoiling of DNA play important roles in carrying out genetic processes such as replication, transcription, recombination etc. Since the discovery of DNA topoisomerase I in 1971 (then named omega protein) in E. coli type I and type II topoisomerases have been found in a wide variety of organisms. In addition the finding that these enzymes are the only ones which can cope with the torsional strain accumulating within the DNA molecules carrying out the genetic processes by swiveling the strands through breakage and rejoining of phosphodiester bonds strongly suggests that they are involved in various aspects of DNA metabolism such as replication, transcription, recombination, differentiation etc. In this article the function of DNA topoisomerases elucidated so far in prokaryotic and eukaryotic cells with special emphasis on their roles in gene expression has been briefly reviewed.