Ubiquitin-Dependent Proteolysis of the Yeast Mating-Type Regulator Matalpha1 Nixon, Christina Erin creator 2009 xiv, 203 p. born digital Thesis (Ph.D.) -- Brown University (2010) Laney, Jeffrey director Landy, Arthur reader Mowry, Kimberly reader Freiman, Richard reader Johnson, Erica reader Brown University. Division of Biology and Medicine. Molecular Biology, Cell Biology, and Biochemistry sponsor theses Cell type in budding yeast is controlled by the master regulatory transcription factors encoded at the mating-type (MAT) locus Mat?1, Mat?2, and Mata1. In homothallic strains, the a and ? haploid cell types are unstable states, and cell type switching can occur with high frequency. To facilitate such efficient switching, the Mat transcription factors are unstable proteins. At least one of these factors, Mat?2, is degraded by the ubiquitin-proteasome system (UPS). It stands to reason that the UPS would also degrade the other ?-specific regulator, Mat?1. Understanding how Mat?1 is degraded and if it is degraded coordinately with Mat?2 will provide a model to study other phenotypic switching events. Here, I demonstrate that Mat?1 is a substrate for the UPS and is targeted for proteolysis by multiple E2 and E3 enzymes, including one common pathway with Mat?2: Ubc4/Ubc5/Slx5-Slx8. Interestingly, Mat?1 turnover requires an intact sumoylation pathway as well as poly-SUMO chains, whereas Mat?2 does not. Using a series of Mat?1 deletion mutants fused to Ura3 (the normally stable uracil biosynthetic enzyme), I have also isolated several regions within Mat?1 that are necessary for rapid turnover potentially corresponding to the multiple ubiquitin ligases. Interestingly, a region coinciding with the alpha1 domain (residues 75-150), while not sufficient to confer wild-type levels of instability to Ura3, is dependent upon Slx5-Slx8. Taken together, these data show that while the degradation pathways of Mat?1 and Mat?2 share commonalities, the details of the pathways are unique for each factor. MATalpha1 ubiquitin-proteasome system protein degradation mating-type switching SUMO Slx5 Slx8 Ufd4 Ubc13 Ubc4 Ubc5 YeastProteolysis RPB 20091218 engEnglish10.7301/Z0M043PCIn CopyrightCollection is open for research.dissertations