Regulated protein degradation by the ubiquitin-proteasome pathway ensures the unidirectionality of mitotic progression by removing cell-cycle regulators required at earlier stages. The APC/C ubiquitin-protein ligase targets proteins by appending polyubiquitin degradation signals that are subsequently recognized by the 26S proteasome. Reporting in this issue, Jin et al. (2008) identify a TEK motif in both ubiquitin and substrates of APC/C that mediates assembly of these degradation signals.