[Biological functions of DNA topoisomerases].

DNA topoisomerases are enzymes involved in various aspects of genetic processes by catalyzing topological changes of DNA. In DNA replication of closed circular DNA, for example, the parental strands are unwound as the synthesis of daughter strands proceed and overwinding and hence positive supercoils are introduced and accumulated in the unreplicated portions of the molecules, which retard and inhibit progression of replication machinery. Analogous situation may often prevail in transcription, recombination etc. within the cells. In order to solve this problem inherent in the metabolism of circular or looped double stranded DNA, living organisms may have evolved the exquisite device of DNA topoisomerases. In the present article biological functions of DNA topoisomerase are briefly reviewed.