Model for UBL protein interfacing with the proteasome. Ddi1 shows a large dependence on the D517 residue of Rpn1 for binding to the proteasome. Additionally, deleting the intrinsic receptor Rpn13 Rpn13, or jointly the ubiquitin binding domains of Rpn13 and Rpn10, results in decreased binding of Dsk2 to the proteasome and reveals a role for the Rpn1-K484 residue in binding UBL proteins. However, Rad23 and the deubiquitinase Ubp6 did not show a dependence on residues D517 nor K484 of Rpn1. It is possible that Rad23 and Ubp6 interaction with the proteasome is stabilized by their interactions with other proteasomal subunits and/or other unidentified residues on Rpn1.