Ubiquitin-Conjugating Enzymes Mediate Essential Functions of the Stress Response
Ubiquitln-mediated proteolysis isamajor pathway for selective protein degradation in eukaryotic cells. This pathway involves the processive covalent attachment of ubiquitin to proteolytic substrates and their subsequent degradation by a specific ATP-dependent protease complex. We have cloned the genes and characterized the function of seven ubiquitin-conjugating enzymes (UBCs) from the yeast Saccharomyces cerevisiae. From this collection, UBC1, UBC4 and UBC5 enzymes were found to mediate degradation of short-lived and abnormal proteins. These enzymes have overlapping functions and constitute a UBC subfamily essential for growth. UBC1 is specifically required at early stages of growth after germination of spores. UBC4 and UBC5 enzymes are heat shock proteins and essential components of the eukaryotic stress response: mutants lacking both UBC4 and UBC5 are unable to grow at elevated temperatures or in the presence of an amino acid analog, constitutively express major heat shock proteins and are constitutively hermotolerant to a severe and acute heat shock.
KeywordsAbnormal Protein Orotic Acid Amino Acid Analog Meiotic Segregation Chronic Heat Stress
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