Identification of a functional docking site in the Rpn1 LRR domain for the UBA-UBL domain protein Ddi1

Background The proteasome is a multi-subunit protein machine that is the final destination for cellular proteins that have been marked for degradation via an ubiquitin (Ub) chain appendage. These ubiquitylated proteins either bind directly to the intrinsic proteasome ubiqutin chain receptors Rpn10, Rpn13, or Rpt5, or are shuttled to the proteasome by Rad23, Dsk2, or Ddi1. The latter proteins share an Ub association domain (UBA) for binding poly-Ub chains and an Ub-like-domain (UBL) for binding to the proteasome. It has been proposed that shuttling receptors dock on the proteasome via Rpn1, but the precise nature of the docking site remains poorly defined.