Identifying targets and function of the ubiquitin related modifier Urm1 in Saccharomyces cerevisiae

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Title: Identifying targets and function of the ubiquitin related modifier Urm1 in Saccharomyces cerevisiae
Author: Kubicek, Charles E., 1981-
Abstract: Post-translational modification of proteins is an important cellular method of controlling various aspects of protein activity, including protein-protein interactions, half- life, and transport. An important class of post-translational modifications involves the ubiquitin family of proteins. In these modifications, a small protein, such as ubiquitin, is conjugated to a target protein through an isopeptide bond. Conjugation by a ubiquitin family member acts as a signal to regulate the activity, function, or stability of the target protein. Urm1, a ubiquitin-like protein conserved throughout all eukaryotes, was initially identified in S. cerevisiae. Loss of Urm1 leads to the disruption of a variety of cellular processes, including oxidative stress response, filamentous growth, and temperature sensitivity. This body of work comprises efforts to identify novel targets of Urm1, the mechanism by which Urm1 is attached to target proteins, and the physiological consequences of such conjugation. To gain understanding of the function and mechanism of Urm1 conjugation, the only known conjugate of Urm1, the peroxiredoxin reductase Ahp1, was examined in an effort to identify the site of modification on Ahp1 and to evaluate the physiological consequences of urmylation of Ahp1. I then completed a series of screens--a synthetic lethal screen, a two-hybrid screen, and a protein over-expression screen--to identify novel Urm1 conjugates and cellular functions dependent on Urm1. Of particular interest were genes identified in the synthetic lethal screen, namely PTC1, which encodes a protein phosphatase, and a set of genes encoding the Elongator complex, which functions in transcriptional elongation and tRNA modification. During this time period, other groups showed that thiolation of tRNAs depends on Urm1. Thus, Urm1 does not function only in protein conjugation, but also as a sulfur carrier in the thiolation of tRNA. Interestingly, I identified Elp2, a component of the Elongator complex, as a new Urm1-conjugate. Because Elp2 is also required for tRNA modification, perhaps Urm1 plays more than one role in tRNA modification. Loss of tRNA modification may disrupt many cellular functions and could explain the variety of urm1 mutant phenotypes. I have determined that all known Urm1 dependent processes are also associated with tRNA modification.
Description: xi, 81 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
Date: 2009-09

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