Many archaea use ESCRT-III to divide, but how is it controlled? In a new publication in Science, the Baum lab shows that the proteasome, which is conserved in both eukaryotes and archaea, is key to the process. It triggers cell division by selectively targeting a structural ESCRT-III filament (purple) at the final stage of cell division, thereby freeing the contractile ESCRT-III filament (green) to constrict the cells.