Post-translational modifications of proteins regulate important physiological and biochemical processes. One such modification is the covalent attachment of the protein ubiquitin. Only a small subset of the roles of ubiquitin- protein conjugation has been characterized in eukaryotes. Ubiquitin's most well-studied role is as a reusable tag marking proteins for proteolysis. In plants, it has been found attached to the photoreceptor phytochrome and the coat protein of Tobacco Mosaic Virus. The purpose of this research is to explore the function of ubiquitin in physiological processes in higher plants. The biochemical analysis examines the subcellular localization of ubiquitin- protein conjugates in Arabidopsis. The molecular analyses of ubiquitin gene expression in higher plants involve 1) isolation of the remaining member(s) of the ubiquitin extension gene family from Arabidopsis, 2) determination of the regulation of expression of different members of the ubiquitin extension gene family and 3) definition of the promoter regions for the ubiquitin extension genes by deletion analysis and site-directed mutagenesis and re- introduction into plants. Ubiquitin is a protein that is widely distributed in plant, animal, yeast and bacterial cells. It is one of the most highly conserved proteins known, having only three amino acid differences between the human and higher plant protein. It serves a number of important biological roles in the cell, the most fully characterized being its role in marking proteins for breakdown, especially abnormal proteins. Current understanding of the regulation of the ubiquitin pathway is rudimentary. Therefore, the goal of these studies is to provide fundamental information on the regulation of the ubiquitin pathway and the regulation of their genes in higher plants.***
