CELL BIOLOGY: Nuclear Waste Disposal

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Science  22 Apr 2005:
Vol. 308, Issue 5721, pp. 468b
DOI: 10.1126/science.308.5721.468b

Quality-control systems within the cytosol are important for the overall health of the cell; aberrant proteins (incorrectly assembled or damaged during use) may not function properly, and the cell has mechanisms for disposing of such waste (and recycling the components) if they cannot be repaired. Gardner et al. find that a similar quality-control system operates within the cell nucleus of the yeast Saccharomyces cerevisiae.

Mutant nuclear proteins are targeted for destruction by the proteasome: a proteolytic machine of the cytosol. A set of nuclear quality-control proteins—San1, which is a ubiquitin-protein ligase, and two ubiquitin-conjugating enzymes, Cdc34 and Ubc1—act together to tag mutant proteins with ubiquitin, the molecular label for proteasomal degradation. San1 possesses a nuclear localization signal that is required for its function, and cells lacking San1 suffer from chronic stress, presumably due to the accumulation of aberrant proteins within the nucleus. Thus, the eukaryotic cell has surveillance and quality-control strategies to protect each of its compartments from the harmful consequences of dysfunctional proteins. — SMH

Cell 120, 803 (2005).

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