DNA topoisomerase I-related function

DNA topoisomerase 1 is a topoisomerase enzyme that catalyzes ATP-independent breakage of single-stranded DNA, followed by passage and rejoining. It catalyzes reaction that leads to the conversion of one topological isomer of DNA to another. Eukaryotic topoisomerase I and II can relax both negative and positive supercoils, whereas prokaryotic enzymes relax only negative supercoils. DNA topoisomerase 1 belongs to the eukaryotic type I topoisomerase family and is a monomer known to interact with SV40 Large T antigen that allows viral DNA replication. It is specifically inhibited by camptothecin (CPT), a plant alkaloid with antitumor activity. It generally has diffuse nuclear localization with some enrichment in nucleoli but on CPT treatment, it is cleared from nucleoli into nucleoplasm. Chromosomal aberration involving DNA topoisomerase 1 is found in a form of therapy-related myelodysplastic syndrome.