Our research focuses on the role of the ubiquitin system in protein degradation. Conjugation to ubiquitin is an obligatory step for protein degradation in eukaryotes. Ubiquitin, a 76-residue protein, is first activated by ubiquitin-activating enzyme in an ATP-consuming reaction and then conjugated to protein substrate by the action of ubiquitin-conjugating enzyme and ubiquitin-protein ligase.  The 26S proteasome, a large multisubunit proteolytic complex that binds ubiquitin-protein conjugate via its chain-binding subunit(s), denatures substrate molecule and degrades it in its catalytic core - the 20S proteasome. Cell surface proteins are degraded by a different mechanism.  Many of them undergo endocytosis and are transported to the vacuole/lysosome where they are destroyed by the vacuolar hydrolases. Numerous plasma membrane proteins have been found to be ubiquitinated, but in most cases, ubiquitination does not lead to their degradation by the 26S proteasome.  The actual function of ubiquitin conjugation to these proteins is not completely clear, but recent data suggest that the ubiquitin tag acts as an internalization signal at the plasma membrane and as an endosomal sorting signal.
         Precise control of protein breakdown by the ubiquitin system is crucial for numerous cellular processes including cell cycle progression, cell growth and proliferation, signal transduction, and transcription. This system has been implicated in several forms of malignancy, in the pathogenesis of several genetic diseases, in immune surveillance/viral pathogenesis, and in chronic degenerative disorders of the nervous system.
         Ubiquitination is a reversible process. Ubiquitin is a stable protein and, therefore, it has to be recycled by the action of deubiquitinating enzymes (DUBs) prior to the degradation of ubiquitin-protein conjugates. Many DUBs have been recently identified in eukaryotic organisms. However, relatively little is known about their physiological functions or natural substrates. Potentially, DUBs may act as negative and positive regulators of the ubiquitin system. In addition to ubiquitin recylcing, they are involved in processing of ubiquitin precursors, in proofreading of protein ubiquitination and in disassembly of inhibitory ubiquitin chains.
          We use a simple eukaryote Saccharomyces cerevisiae as a model system because it provides the possibility, at a level not yet available in any other eukaryotic organism, of both genetic manipulation and detailed biochemical analysis. Given the high degree of conservation of fundamental metabolic systems between yeast and higher eukaryotes in general, the results of our research will provide important insights into selective protein degradation in other eukaryotes as well. Our long-term goal is to identify and to characterize particular members of the yeast DUB family that are responsible for each step of ubiquitin homeostasis in the eukaryotic cell.