The SUMO system: a master organizer of nuclear protein assemblies.

Cellular signaling pathways largely depend on the plasticity of multiprotein complexes. A central mechanism that assures the coordinated assembly and disassembly of protein complexes is the reversible post-translational modification of the individual components for example by phosphorylation, acetylation, or ubiquitylation. Accumulating evidence indicates that the small ubiquitin-related modifier (SUMO) system is another master organizer of protein complexes. Here, we will focus on the role of SUMO in the regulation of nuclear protein complexes that are involved in chromatin remodeling, double-strand break repair, and ribosome biogenesis. On the basis of these selected pathways, we will summarize current ideas of SUMO signaling, including the concept of group modification and the intersection of the ubiquitin and SUMO pathways.