Pup grows up: in vitro characterization of the degradation of pupylated proteins.

By reconstituting the recently discovered prokaryotic ubiquitin-like protein (Pup)--proteasome degradation system in vitro, Weber-Ban and colleagues (Striebel et al, 2010) elucidate its mechanism and describe a surprising variation on the established principles of protease targeting. Nevertheless, their findings suggest that the bacterial and eukaryotic systems follow the same overall principles even if the details differ.