Definition of topoisomerase in US English:



  • An enzyme which alters the supercoiled form of a DNA molecule.

    • ‘Since topoisomerase activity is needed for replication, inhibition of topoisomerases might prevent replication in irradiated S phase cells, avoiding DNA synthesis upon a damaged template.’
    • ‘Topoisomerase III is a type I topoisomerase, acting on DNA that is negatively supercoiled and/or contains single-strand regions.’
    • ‘Both topoisomerase I and RNA polymerase II reactivity occurs in the minor groove of DNA.’
    • ‘DNA topoisomerase I may play a major role in transcription; the enzyme is physically associated with actively transcribed regions of chromatin where it reduces torsional stress generated during transcription.’
    • ‘Irinotecan is a camptothecin analogue that acts through the inhibition of a DNA unwinding enzyme, topoisomerase I, resulting in replication arrest with breaks in single strand DNA.’
    • ‘Down-regulated topoisomerase II gene expression in etoposide-selected cells has also been shown to be associated with an increased rate of spontaneous polyploidization.’
    • ‘AQ4 is a potent topoisomerase II inhibitor and DNA intercalator.’
    • ‘These compounds stabilize and trap the topoisomerase I - DNA complex, preventing the religation step of the breakage/rejoining reaction mediated by the enzyme.’
    • ‘The clastogenicity of topoisomerase inhibitors is believed to result from the transient stabilization of the topoisomerase enzyme with DNA during the catalytic cycle.’
    • ‘The value for the ancestor was expressed relative to the midpoint topoisomer of plasmid that was completely relaxed by using calf-thymus topoisomerase I and assigned = 0.’
    • ‘Among the genes affected by supercoiling are the topoisomerase genes.’
    • ‘An in vitro study showed that the collision between a moving replication fork and a stalled topoisomerase can convert the complex to a nonreversible form.’
    • ‘Further, the broken site at the TT4 gene contained a potential topoisomerase I cleavage site.’
    • ‘Taken together, these results indicate that the overexpression of the topoisomerase I gene causes DNA damage that is lethal only in the scaA - background.’
    • ‘Finally, the in vivo catalytic activities of eukarytotic type IA topoisomerases, the topoisomerase III from various higher organisms may be related to their sequences.’
    • ‘This study illuminates some of the similarities and differences in the topoisomerase / DNA complex in eukaryotes and prokaryotes.’
    • ‘DNA topoisomerase II is an essential cellular enzyme that functions in the segregation of chromosome pairs and in chromosome condensation.’
    • ‘Recent studies in Xenopus have shown a role for DNA replication in the recruitment of topoisomerase II to the chromosomes to facilitate condensin assembly and condensation.’
    • ‘A heart-shaped molecular donut, the topoisomerase II dimer boasts an electropositive tunnel, the likely passage point for DNA.’
    • ‘In certain cases, the combination of a helicase and a topoisomerase provides a unique biological function and the interaction between the two is evolutionarily conserved.’


1970s: from Greek topos ‘place’ + isomer + -ase.