The anaphase inhibitor Pds1 binds to the APC/C-associated protein Cdc20 ina destruction box-dependent manner

An essential aspect of progression through mitosis is the sequential degrad ation of key mitotic regulators in a process that is mediated by the anapha se promoting complex/cyclosome (APC/C) ubiquitin ligase [1]. In mitotic cel ls, two forms of the APC/C exist, ApC/C-Cdc10 and ApC/C-Cdh1, which differ in their associated WD-repeat proteins (Cdc20 and Cdh1, respectively), time of activation, and substrate specificity [2, 3]. How the WD-repeat protein s contribute to APC/C's activation and substrate specificity is not clear. Many APC/C substrates contain a destruction box element that is necessary f or their ubiquitination [4-6]. One such APC/C substrate, the budding yeast anaphase inhibitor Pds1 (securin), is degraded prior to anaphase initiation in a destruction box and APC/ C-Cdc20-dependent manner [3, 7]. Here we fin d that Pds1 interacts directly with Cdc20 and that this interaction require s Pds1's destruction box. Our results suggest that Cdc20 provides a link be tween the substrate and the core APC/C and that the destruction box is esse ntial for efficient Cdc20-substrate interaction. We also find that Pds1 doe s not interact with Cdh1. Finally, the effect of spindle assembly checkpoin t activation, known to inhibit APC/C function [8], on the Pds1-Cdc20 intera ction is examined.