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

Protein quality control systems, which fix or rid the cell of unfolded, misfolded, or improperly modified proteins, have long been known to exist both in prokaryotes and eukaryotes. But they have been found only in compartments where protein synthesis occurs: the cytoplasm, the endoplasmic reticulum, and the mitochondria, senior author Dan Gottschling, of Seattle's Fred Hutchinson Cancer Research Center, told The Scientist.

"It largely has been thought that as proteins are being made, they're being sampled and destroyed right during the process of folding and assembly," said Gottschling. "We wanted to find a place where proteins that become old could be recognized and degraded, and the nucleus is the only...

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