Methods to study SUMO dynamics in yeast

Covalent modification of proteins with the small ubiquitin-related modifier (SUMO) is found in all eukaryotes and is involved in many important processes. SUMO attachment may change interaction properties, subcellular localization, or stability of a modified protein. Usually, only a small fraction of a protein is modified at a given time because sumoylation is a highly dynamic process. The sumoylated state of a protein is controlled by the activity of the sumoylation enzymes that promote either their mono- or poly-sumoylation (SUMO chain formation), by SUMO proteases that reverse these modifications, and by SUMO-targeted ubiquitin ligases (STUbL, ULS) that mediate their degradation by the proteasome. While some organisms, such as humans, express multiple isoforms, budding yeast SUMO is encoded by a single and essential gene termed SMT3. The analysis of the simpler SUMO system in budding yeast has been instrumental in the identification of enzymes acting on this modification and controlling its dynamics. Sumoylation of proteins changes dramatically during the cell division cycle and under various stress conditions. Here we summarize various approaches that employ Saccharomyces cerevisiae as a model system to study the dynamics of sumoylation and how it is controlled.