The aim of this work is to demonstrate the role of SUMO (Small Ubiquitin like MOdifier) in synaptic plasticity. Specifically, my goal is to show that synaptic kainate receptors (KARs) are regulated in an activity-dependent manner that involves their SUMOylation. Recently, Mellor and Henley have discovered that the KAR subunit GluR6 is a substrate for SUMO and that SUMOylation of GluR6 causes KARs to be endocytosed. This was demonstrated for synaptic KARs at mossy fibre synapses in the hippocampus, suggesting that it is a mechanism for activity-dependent regulation of KARs at this synapse. In the post-synaptic density, PDZ-domain-containing proteins play a prominent role in organizing synaptic elements. My hypothesis is that SUMOylation of GluR6 influences the interaction of KARs with PDZ binding proteins, thus leading to KAR plasticity. In addition, phosphorylation of GluR6 by protein kinase C (PKC) could potentially regulate SUMOylation itself. To test these hypotheses, I intend to employ electrophysiological techniques (patch-clamp recording) in acute and cultured thalamocortical and hippocampal slices, combining them with biochemical techniques to block specific protein-protein interactions and modulate the level of GluR6 SUMOylation. Since the role of SUMOylation is largely unknown outside of the nucleus, its involvement in synaptic plasticity constitutes a major new function for SUMO. Therefore, SUMOylation provides a novel and intriguing mechanism underlying synaptic plasticity.