Ubiquitin is a common demoninator in the targeting of substrates to all three major protein
degradation pathways in mammalian cells: the proteasome, the lysosome, and the
autophagosome. The factors that direct a substrate toward a particular route of degradation
likely include ubiquitin chain length and linkage type, which may favor interaction with
particular receptors or confer differential susceptibility to deubiquitinase activities associated
with each pathway.