Topoisomerase I (TOP1)

DNA topoisomerase 1 is a DNA topoisomerase, an enzyme that controls and alters the topologic states of DNA during transcription. This enzyme catalyzes the transient breaking and rejoining of a single strand of DNA which allows the strands to pass through one another, thus altering the topology of DNA. This gene is localized to chromosome 20 and has pseudogenes which reside on chromosomes 1 and 22.Type IA topoisomerases creates a single break in DNA, and passes a second strand or duplex through the break. This strand passage mechanism shares several features with type IIA topoisomerases. They both form a 5' phosphotyrosine intermediate, and require a divalent metal ion to perform its work. Unlike type II topoisomerases, type IA topoisomerases do not use energy to do its work .