Formation mechanism of proteasome granules

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The proteasome is an ATP-dependent protease complex responsible for targeted protein degradation in eukaryotic cells. To identify factors that affect the proteasome dynamics, we screened a yeast mutant library and found that the proteasome formed a large cytoplasmic granule in almost all the mitochondrial mutants. We found that lowered cellular ATP levels induce the granule formation of the proteasome even in the wild-type cells. Importantly, the granule formation of the proteasome is conserved in yeast and humans. Furthermore, the purified proteasomes formed fibrous aggregated structures by ATP depletion. Taken together, these results suggest that the proteasome itself senses cellular ATP levels and autonomously forms reversible granule structure in responding to cellular environments.