Background

We use yeast as a model system to study protein degradation via the ubiquitin-proteasome system, using genetic and biochemical approaches. Our model substrate is the mating switch endonuclease of yeast, Ho endonuclease. Ho is a nuclear protein, however, it must be exported to the cytoplasm to be degraded. We have identified the protein kinases of the DNA damage response pathway of yeast that mark Ho for degradation, the receptor that recruits Ho for ubiquitylation and further downstream functions that are important for its recruitment by the proteasome. In addition, we have studied nuclear import and export of Ho in detail. Furthermore, we have established a yeast model of a human disease that involves a mutation in a microtuble chaperone protein. This protein, Pac2, binds the proteasomes and microtubules and we are exploring a possible role in subcellular localization of proteasomes.

Current Projects

1. Nuclear protein quality control: How are misfolded proteins eliminated in the nucleus? We have made probes for studying the degradation of soluble proteins and of proteins bound to the inner nuclear membrane.

2. Subcellular localization of proteasomes: We are using yeast mutants to study this in cells in which a particular subunit of the proteasome is labelled with a fluorescent tag.

3. The stress response in eukaryote cells: We have reporter proteins or we measure mRNA directly after a series of different stresses in wild type cells and in mutants in which a specific stress transducer is absent. Our aim is to determine how different stress transduction modules communicate with each other.

4. Interdisciplinary project with Dr Oleg Krichevsky of the Physics Department. We use high sensitivity microscopy to follow the dynamic response to stress in single cells at the levels of mRNA and of synthesis of specific reporter proteins. We also execute experiments in vitro to determine how a transcription factor homes in on its binding site in the gene promoter.

Voloshin O. and Raveh, D. 2012 Handover of Ho Endonuclease and Ufo1 to the Proteasome by the UbL-UbA Shuttle Protein, Ddi1, Analysed by Complex Formation In Vitro. PLoS One 7(7):e39210.

Lavut A. and Raveh, D. 2012 Sequestration of Highly Expressed mRNAs in Cytoplasmic Granules, P-Bodies, and Stress Granules Enhances Cell Viability.
PLoS Genet 8(2): e1002527.

Bakhrat A, Eltzov E, FinkelsteinY, Marks RS, Raveh D. 2011 UV and arsenate toxicity: a specific and sensitive bioluminescence assay. Cell Biol Toxicol. 27:227-236.

Voloshin O, Gocheva Y, Gutnick M, Movshovich N, Bakhrat A, Baranes-Bachar K, Bar-Zvi D, Parvari R, Gheber L and Raveh D. 2010 Tubulin Chaperone E Binds Microtubules and Proteasomes and Protects Against Misfolded Protein Stress.
Cell Mol Life Sci. 67:2025-38.

Bakhrat, A., Krichevsky, O., Rom, I., Gabriel Schlenstedt, G., Pietrokovski, S. and Raveh, D. 2006. An efficient nuclear import system was an early adaptation in evolution of yeast Ho endonuclease from an intein ancestor.
J. Biol. Chem. 281:12218-12226.

Ph.D. Weizmann Institute of Science, 1976