The Deubiquitylating Enzyme Ubp12 Regulates Rad23-Dependent Substrate Delivery at the Proteasome

Abstract

The consecutive actions of the ubiquitin-selective segregase Cdc48 and the ubiquitin shuttle factor Rad23 result in the delivery of ubiquitylated proteins at the proteasome. Here, we show that the deubiquitylating enzyme Ubp12 interacts with Cdc48 and regulates proteasomal degradation of Rad23-dependent substrates. Overexpression of Ubp12 results in stabilization of Rad23-dependent substrates. We show that Ubp12 removes short ubiquitin chains from the N-terminal ubiquitin-like domain (UbL) of Rad23. Preventing ubiquitylation of Rad23 by substitution of lysine residues within the UbL domain, Rad23UbLK0, does not affect the non-proteolytic role of Rad23 in DNA repair but causes an increase in ubiquitylated cargo bound to the UBA2 domains of Rad23 and recapitulates the stabilization of Rad23-dependent substrates observed upon overexpression of Ubp12. Expression of Rad23UbLK0 or overexpression of Ubp12 impairs the ability of yeast to cope with proteotoxic stress consistent with inefficient clearance of misfolded proteins by the ubiquitin/proteasome system. Our data suggest that ubiquitylation of Rad23 plays a stimulatory role in facilitating the transfer of ubiquitylated substrates to the proteasome.\n\nSummary statementUbiquitylation of a ubiquitin shuttle factor regulates the delivery of substrates at the proteasome, uncovering a novel regulatory link between ubiquitin and proteasomal degradation.