resolvases

Resolvases are enzymes that resolve branched DNA structures, especially Holliday junctions, which arise during homologous recombination and various DNA repair processes. They catalyze strand cleavages that convert four-stranded DNA intermediates into two intact duplex molecules, enabling proper ligation and chromosome segregation. Resolvases can belong to different families and operate in different cellular contexts, but all aim to resolve joint DNA structures to restore normal DNA duplex continuity.

Two broad categories are often recognized. Structure-specific resolvases act directly on branched DNA junctions, cutting across the junction with coordinated incisions to produce usable DNA ends. Site-specific recombinases, though primarily involved in controlled DNA rearrangements, can also function as resolvases in certain contexts by resolving cointegrates or complex intermediates generated during recombination. In addition, some enzymes participate in resolution as part of larger nuclease complexes that recognize a range of DNA structures rather than strictly defined sites.

In bacteria, the classical Holliday junction resolvase is RuvC, which forms active dimers that perform symmetrical cuts in the junction. Other bacterial and archaeal enzymes, such as members of the Hjc family, also function as Holliday junction nucleases in various organisms. In eukaryotes, resolution involves multi-subunit complexes such as GEN1/Yen1 and the MUS81-EME1 and SLX1-SLX4 nucleases, which together address Holliday junctions and other branched structures that arise during DNA replication and repair.

Biological significance lies in maintaining genome stability and ensuring accurate chromosome segregation after recombination. Defects in resolvases can lead to unresolved DNA intermediates, chromosomal instability, and heightened sensitivity to DNA damage.