Proteolysis: anytime, any place, anywhere?

Proteolysis via the ubiquitin-proteasome system (UPS) is a rapid and effective method of degrading a specific protein at a specific time, and in many cases a protein is degraded only in response to a particular cellular signal or event. However, an added dimension to the control of protein degradation is possible because the ubiquitin system can be spatially regulated. Controlling where a protein is degraded can enhance the specificity and timing of proteolysis, generate asymmetry and maintain sub-compartments even in the mitotic cell. Here, we discuss this aspect of the UPS.