Pupylation versus ubiquitylation: tagging for proteasome‐dependent degradation

P rokaryotic u biquitin‐like p rotein (Pup) is the first identified prokaryotic protein that is functionally analogous to ubiquitin. Despite using the proteasome as the end‐point for proteolysis, Pup differs from ubiquitin both biochemically and structurally. We will discuss these differences that have been highlighted by several recent studies. Finally, we will speculate on the possible interactions between the two analogous pathways in pathogen and host.