A ubiquitin-interacting motif conserved in components of the proteasomal and lysosomal protein degradation systems

Ubiquitination generally serves as a signal for targeting cytoplasmic and n uclear proteins to the proteasome for subsequent degradation. Recently, evi dence has accumulated indicating that ubiquitination also plays an importan t role in targeting integral membrane proteins for degradation by the lytic vacuole or the lysosome. This article describes a conserved protein motif, based on a sequence of the proteasomal component Rpn10/S5a, that is known to recognize ubiquitin. The presence of this motif in Eps15, Epsin and HRS, proteins involved in ligand-activated receptor endocytosis and degradation , suggest a more general role in ubiquitin recognition.