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Selective Degradation of Abnormal Proteins in Mammalian Tissue Culture Cells

Mario R. Capecchi, Nancy E. Capecchi, Stephen H. Hughes and Geoffrey M. Wahl
Proceedings of the National Academy of Sciences of the United States of America
Vol. 71, No. 12 (Dec., 1974), pp. 4732-4736
Stable URL: http://www.jstor.org/stable/63900
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.
Selective Degradation of Abnormal Proteins in Mammalian Tissue Culture Cells
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Abstract

The degradation rates of several missense mutants of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) in mouse L cells are compared to those of the wild-type enzyme. Although the rates of total protein breakdown in the mutant cell lines are identical to that of the parental L cell line, defective molecules of hypoxanthine-guanine phosphoribosyltransferase present in the mutant cell lines are degraded much faster than the wild-type enzyme. The level of defective phosphoribosyltransferase molecules present in the mutant cell lines is inversely proportional to the breakdown rate. This observation indicates that the major factor determining the concentrations of the defective phosphoribosyltransferases is their specific degradation rate. These results strongly support the hypothesis that abnormal proteins are selectively degraded in mammalian cells.

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