Now online! Structural steps along the assembly of proteasome storage granules—membraneless organelles that form in response to metabolic shifts in yeast—are visualized inside cells by cryo-electron tomography. Inactive 26S proteasomes oligomerize into trimers, which assemble into paracrystalline arrays that serve as reservoirs of fully assembled proteasomes under conditions of low energy, ready for reactivation when glucose is restored.