SUMO-1 possesses DNA binding activity

Using NMR spectroscopy and protein-DNA cross-linking experiments, we demonstrate here that SUMO-1 can specifically interact with dsDNA in a sequence-independent fashion. We also show that SUMO-1 binding to DNA can compete with other protein-DNA interactions at the example of the regulatory domain of Thymine-DNA Glycosylase and, based on these competition studies, estimate the DNA binding constant of SUMO1 in the range 1 mM.This finding provides an important insight into how SUMO-1 might exert its activity. SUMO-1 might play a general role in destabilizing DNA bound protein complexes thereby operating in a bottle-opener way of fashion, explaining its pivotal role in regulating the activity of many central transcription and DNA repair complexes.Ubiquitin and small ubiquitin-like modifiers (SUMOs) form a family of structurally related proteins that often become covalently attached to other cellular factors. This post-translational modification of proteins, usually on lysine residues, with ubiquitin and SUMOs changes the functional properties of their targets [1-15]. Both, the regulation of the target's enzymatic activity and the modification of interaction patterns with third partners such as proteins and DNA have been described. Thereby, sumoylation apparently also provides a means to recruit SUMO interacting proteins via their SUMO binding motifs (SBMs) to the sumoylated target [16]. Furthermore, sumoylation and SUMO association have been found to influence other post-translational modifications such as phosphorylation. Sumoylation is an energy-dependent process carried out by a dedicated enzymatic machinery which is similar in composition and activity to the ubiquitination apparatus [2-7,9,10]. SUMO-specific proteases (SENPs) can reverse the process of sumoylation. Sumoylation has an essential role in most organisms. Deletion or inactivation of SUMOs or enzymes involved in the sumoylation process lead to severe growth defects in yeast or embryonic lethality in mice