2 Mechanizm topoizomerazy IA

a Typc IA topoisomerase mcchanism b Typc IB topoiiomcrasc mechanism

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Type I topoisomerase mechanisms

a | Type lAtopoisomerases pass a single-stranded DNA segment (yellow) through a transient break in a second single DNA strand (green). The structure of Escherichia coli topo III (a type IA topoisomerase) bound to single-stranded DNA is shown on the right^. b j Type IB topoisomerases nick one DNA strand (green), allowing one duplex end to rotate with respect to the other around the remaining phosphodiester bond (yellow). The structure of human topo IB bound to duplex DNA is shown on the right