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Date of Award

4-25-1997

Document Type

Restricted Thesis: Campus only access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Dr. Valerie M. Kish

Abstract

Chlamydomonas reinhardtii has long been the subject of extensive genetic, cellular, and biochemical study. A unicellular green alga capable of photosynthesis, the organism is simple and inexpensive to grow and maintain. The biflagellate alga has been a model organism in the study of flagellar synthesis and disassembly. The life cycle has been well characterized through years of study on both the diploid vegetative stage and the haploid gametic phase. Gametogenesis, mating, and gamete fusion is now well understood. The use of Chlamydomonas reinhardtii as a system offers a solid foundation of knowledge on which to build a study of ubiquitin and the heat shock response.

Ubiquitin is one protein that has been shown to have altered expression in response to cellular stress. This has been hypothesized before due to ubiquitin's role in the ubiquitin-proteosome proteolytic pathway. Present in almost every eukaryotic organism studied to date, this physiologic pathway is constantly cycling proteins and amino acids. Highly conserved cellular enzymes (El, E2, and E3) are responsible for the recognition of proteins doomed for degradation. Once a protein is recognized, the enzymes covalently conjugate a small (76 amino acid) ubiquitin protein onto the original protein forming a ubiquitin conjugate. Although a single ubiquitin tag may be sufficient to target a protein for degradation, it more often requires the conjugation of several proteins in linear or branched chains. The ubiquitin conjugation signals the protein's degradation by the 26S proteosome.

In the constant cycling of proteins and amino acid subunits, the ubiquitin-proteosome system has been shown to be involved in the regulation of essential cellular events such as cell division, DNA repair, and antigen presentation. This cycling is also essential in the heat shock response. Increased temperatures, and other environmental stresses, are known to cause protein denaturation. Denatured, non-functional proteins must quickly be degraded freeing their amino acids for use in the synthesis of functional proteins. These new proteins may replace the damaged proteins or may be new heat shock proteins enabling the cell to survive the stressful event. The importance of the heat shock response and heat shock proteins to cellular survival under adverse conditions makes their study biologically and medically relevant The high degree of protein conservation across all organisms makes answering difficult questions easier through the use of well understood model organisms like Chlamydomonas reinhardtii. Ubiquitin is also well conserved, differing by only two of the 76 amino acids in the human and yeast protein. Recent research has contributed a great deal to a broader understanding of the many cellular roles of ubiquitin. Therefore analysis of ubiquitin in Chlamydomonas reinhardtii and the role of ubiquitin in the stress response of the organism is an important issue. Research is possible due to the breadth and depth of information available regarding the organism and ubiquitin.

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