Researchers have discovered the first protein quality control system in the yeast nucleus. They report that the system involves an ubiquitin-protein ligase that specifically targets four distinct mutant nuclear proteins for destruction by the proteasome.1

Protein quality control systems have long been known to exist both in prokaryotes and eukaryotes, but only in compartments where protein synthesis occurs, says coauthor Dan Gottschling of Seattle's Fred Hutchinson Cancer Research Center. "We wanted to find a place where proteins that become old could be recognized and degraded," he says, "and the nucleus is the only compartment in which that could potentially happen."

Their approach was a smart one, according to Christian Hirsch of the Max-Delbrück Center for Molecular Medicine. "They looked at screens that had found suppressors of temperature-sensitive mutant proteins that are functional in the cell, but that are degraded because they are recognized by a quality control system," says...

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