Resolvase is an enzyme that allows two chromosomes to cross over and is therefore essential to enable offspring to inherit a unique mixture of traits from their parents. Several resolvases are known in bacteria, but none have been isolated from eukaryotic cells. But, two papers published simultaneously in November Cell and Molecular Cell by teams at The Scripps Research Institute, La Jolla, California, identify Mus81 — a protein related to a repair endonuclease — as a resolvase enzyme that is found in both in the yeast, and in humans.

Working with Schizosaccharomyces pombe, Michael Boddy and colleagues observed that Mus81 and Eme1 proteins are components of an endonuclease that resolves X-shaped DNA structures (Holliday junctions) into linear duplex products. Mus81 and Eme1 are required at a late step of meiotic recombination (Cell 2001, 10.1016/S009296740105335).

In the second paper, Xiao-Bo Chen and colleagues found that human Mus81 resolves...