UPS shipping and handling

It is now clear that the two broad sets of reactions in the ubiquitin-proteasome system (UPS), the conjugative and degradative steps, are intricately coupled in vivo and that there are numerous factors that aid in the handling and delivery of ubiquitylated proteins to the proteasome. The report from Richly et al (2005)this issue of Cell]) suggests how several of the known players in this process might work together in guiding and delivering some substrates to their final destinations.