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Ubiquitin Has Intrinsic Proteolytic Activity: Implications for Cellular Regulation

Victor A. Fried, Harry T. Smith, Ellen Hildebrandt and Kristi Weiner
Proceedings of the National Academy of Sciences of the United States of America
Vol. 84, No. 11 (Jun. 1, 1987), pp. 3685-3689
Stable URL: http://www.jstor.org/stable/29463
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Ubiquitin Has Intrinsic Proteolytic Activity: Implications for Cellular Regulation
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Abstract

Ubiquitin is a protein of 76 amino acids found in every eukaryotic cell. Although ubiquitin is implicated in ATP-dependent nonlysosomal protein degradation and is also conjugated to specific cellular proteins, the role played by ubiquitin in cellular events has not been defined. We report that purified ubiquitin has intrinsic proteolytic activity and demonstrate that this activity is comparable to that of other well-characterized proteases. Monoclonal antibodies specific to ubiquitin inhibit proteolysis. Ubiquitin has protease activity over a broad pH range with an optimum at pH 8.0. It is stimulated by Ca2+ and is inhibited by high concentrations of phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate. Ubiquitin will cleave proteins at a limited number of sites. We propose that the ubiquitination of a protein can convert that protein into an ad hoc specific protease and models are presented as to how this can play a role in regulating a variety of cellular events.

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