TI - The CDH1 protein in APC complex binds to HEF1 . AB - To be ubiquitinated and thus degraded by the proteasome pathway , APC subSTRates need first to be recognized by either CDC20 or CDH1 which targets the ligase to specific SUBstrates during metaphase-anaphase transition as well as during late anaphase , respectively [29,35,36] . Recent studies have demonstrated the direct binding between APC SUBstrates and CDC20 or CDH1 [37] . CDH1 has also been shown to bind to the other Smad3 interactor SnoN in Smad3 -regulated SnoN ubiquitination [18,19] . We thus also examined whether CDH1 interacts with HEF1 , by the direct binding test in vitro . Either GST-HEF1 or GST alone as a control were incubated with in vitro translated 35S-labeled CDH1 . As shown in Figure 4A , in vitro translated CDH1 binds to GST-HEF1 , suggesting a possible role of CDH1 in targeting HEF1 for APC -mediated ubiquitination of HEF1 .