decatenates

Decatenation is the enzymatic process of separating interlinked circular DNA molecules (catenanes) into individual molecules. It is especially important after replication of circular genomes such as bacterial chromosomes and plasmids, where the two daughter circles can remain interlinked.

Mechanism: In bacteria, DNA decatenation is mainly performed by type II topoisomerases, notably topoisomerase IV. In eukaryotes, type II topoisomerases (Topo IIα and Topo IIβ) perform decatenation, especially during mitosis. These enzymes induce transient double-strand breaks in one DNA duplex, pass another duplex through the break, and reseal, using ATP hydrolysis. This reaction separates catenanes and also resolves supercoils.

Context: Efficient decatenation is essential for chromosome segregation and cell division. In bacteria, failure to decatenate can block plasmid and chromosome separation. In eukaryotic cells, decatenation occurs during late mitosis and is coordinated with sister chromatid cohesion release. Inhibitors of topoisomerase II, including certain anticancer drugs (etoposide, doxorubicin) and antibiotics, selectively increase DNA breaks and impede decatenation.

Note: Decatenation is distinct from general DNA relaxation or knotting; it specifically resolves interlinked circular molecules.