Mechanisms of RING E3 ligase regulation in Arabidopsis

Abstract

Ubiquitination is the posttranslational modification of selected proteins by the covalent attachment of one or more ubiquitin molecules. The biological importance of protein ubiquitination is reflected in the fact that disruption of the conjugation pathway leads to developmental aberrations, abnormal responses to stimuli and defects in cell division and growth. At the center of the conjugation cascade is the substrate recruiting E3 ligase, which largely governs specificity. Although the role of E3 ligases in selectively controlling protein abundance, localization and activity is well studied, many aspects of E3 ligase regulation needs to be elucidated. The aim of this proposal is to understand the mechanism of E3 ligase activity regulation in response to external stimuli via analysis of KEG, a novel Arabidopsis RING E3. KEG is active as a E3 ligase and kinase, capable of post-translationally modifying one or more proteins, including itself, by ubiquitination and/or phosphorylation. The precise roles that these modifications play in the regulation of KEG function will be investigated. KEG is a negative regulator of ABA signaling, a major phytohormone which plays a key role in plant development and survival under stressful conditions. A combination of in vivo and in vitro approaches will be used to define the mechanism by which ABA signaling modulates KEG E3 ligase and/or kinase activity to control protein ubiquitination and subsequent degradation by the 26S proteasome.