DNA topoisomerases are nuclear enzymes that regulate the topological structure of DNA by transiently breaking and rejoining DNA strands. Although DNA topoisomerase I and DNA topoisomerase II relax both positive and negative supercoils, DNA topoisomerase III relaxes only negative supercoils. DNA topoisomerase III alpha exists as a long and a short isoform, which are produced by alternative splicing. DNA topoisomerase III alpha, which localizes to the nucleolus, is constitutively expressed and remains at high levels throughout the cell cycle in HL-60 cells. DNA topoisomerase III beta exists as three isoforms, namely beta1, beta2 and beta3, also produced by alternative splicing. DNA topoisomerase III beta1 is expressed in testes, heart and skeletal muscle, whereas beta2 is expressed in thymus, kidney and pancreas.
DNA topoisomerase 3-beta-1; DNA topoisomerase III beta-1; TOP3B; TOP3B1; Topo III beta; topoisomerase III beta