DNAtopoisomeraasi

DNAtopoisomeraasi refers to DNA topoisomerases, a family of enzymes that regulate the topology of DNA by forming transient covalent bonds to the DNA backbone. They relieve or introduce supercoils during essential cellular processes such as replication, transcription, recombination, and DNA repair, ensuring that the double helix can be unwound and rewound as needed.

Topoisomerases are divided into two main types. Type I enzymes cleave one strand of the DNA, changing the linking number by increments of one without requiring ATP in their catalytic steps. Type II enzymes cleave both strands, changing the linking number by two and typically require ATP hydrolysis to power strand passage.

Within type I, subtypes IA and IB differ in mechanism. Type IA forms a 5'-phosphotyrosyl intermediate and relieves supercoils by passing a single strand through the break. Type IB forms a 3'-phosphotyrosyl intermediate and uses a controlled rotation mechanism to relax DNA. Eukaryotes primarily use type IB Top1, whereas bacteria carry type IA and type II enzymes as well.

In cells, topoisomerases maintain genome stability by removing torsional stress ahead of replication forks and transcription complexes. They are targets for anticancer drugs: camptothecin and its derivatives inhibit Top1 by stabilizing the cleavage complex, whereas other drugs target type II enzymes such as topoisomerase II. The discovery of topoisomerases is attributed to James Wang in the 1970s.

DNAtopoisomeraasi thus denotes the conserved function of maintaining proper DNA supercoiling across organisms, which is essential for genome expression and integrity.