The Nse2/Mms21 SUMO ligase of the Smc5/6 complex in the maintenance of genome stability

There exist three highly-conserved structural maintenance of chromosomes (Smc) complexes that ensure genome stability during eukaryotic cell division. There are the well-characterized cohesin and condensin complexes and the third Smc complex, Smc5/6. Nse2/Mms21, a SUMO ligase, is a component of the Smc5/6 complex and recent data have indicated that Nse1 may function as a ubiquitin ligase. Smc5/6 regulates sister chromatid cohesion, homologous recombination and chromatin structure and conformation. This review examines the functions of Smc5/6 in DNA repair and the maintenance of genomic integrity and explores the roles of the associated SUMO and ubiquitin ligases. Recent findings have indicated that Smc5/6 may play a topological role in chromosome dynamics, which may help understand the complexity of its activities.