Ubiquitin-mediated proteolysis of a short-lived regulatory protein depends on its cellular localization.
In this study we demonstrate that the Deg1 degradation signal of the transcriptional repressor Matalpha2 confers compartment-specific turnover to a reporter protein. Rapid degradation of a Deg1-containing fusion protein is observed only when the reporter is efficiently imported into the nucleus. In contrast, a reporter that is constantly exported from the nucleus exhibits an extended half-life. Furthermore, nuclear import functions are crucial for both Deg1-induced degradation as well as for the turnover of the endogenous Matalpha2 protein. The conjugation of ubiquitin to a Deg1-containing reporter protein is abrogated in mutants affected in nuclear import. Obviously, the Deg1 signal initiates rapid proteolysis within the nucleoplasm, whereas in the cytosol it mediates turnover via a slower pathway. In both pathways the ubiquitin-conjugating enzymes Ubc6p/Ubc7p play a pivotal role. These observations imply that both the cellular targeting of a substrate and the compartment-specific activity of components of the ubiquitin-proteasome system define the half-life of naturally short-lived proteins.
Lenk
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Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Strasse 10, Berlin 13092, Germany.
Sommer
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D002352:Carrier Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D018398:Homeodomain Proteins / Q000378:metabolism*; D019751:Intramolecular Transferases; D007700:Kinetics; D008025:Ligases / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013997:Time Factors; D014158:Transcription, Genetic; D044763:Ubiquitin-Conjugating Enzymes; D014452:Ubiquitins / Q000378:metabolism*
C109280:CUE1 protein, S cerevisiae; D002352:Carrier Proteins; D005656:Fungal Proteins; D018398:Homeodomain Proteins; D008164:Luminescent Proteins; C062928:MATA2 protein, S cerevisiae; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D049452:Green Fluorescent Proteins; C082461:UBC6 protein, S cerevisiae; C489967:UBE2J1 protein, human; C079437:UBE2L3 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D019751:Intramolecular Transferases; C068903:DEG1 protein, S cerevisiae; D008025:Ligases