Small ubiquitin-like modifier (SUMO) is a small molecule, but has a variety of regulatory functions in cells. SUMO modification is involved in transcriptional regulation, subcellular localization, and protein-protein interactions. SUMO conjugation requires sequential E1-dependent activation, E2-dependent conjugation, and E3-dependent ligation steps. Protocol includes: In vivo and in vitro SUMOylation assay and deSUMOylation assay. - [Read Sumoylation and Desumoylation Assays for a Chromatin-Remodelling Complex In Vivo and In Vitro]