Rpn10p is a receptor for ubiquitinated gcn4p in proteasomal proteolysis

Abstract

GCN4 is a typical eukaryotic transcriptional activator that is implicated in the expression of many genes involved in amino acids and purine biosyntheses under stress conditions. It is degraded by 26S proteasomes following ubiquitination. However, the immediate receptor for ubiquitinated Gcn4p has not yet been identified. We investigated whether ubiquitinated Gcn4p binds directly to Rpn10p as the ubiquitinated substrate receptor of the 26S proteasome. We found that the level of Gcn4p increased in cells deleted for Rpn10p but not in cells deleted for RAD23 and DSK2, the other ubiquitinated substrate receptors and, unlike RpnIOp, neither of these proteins recognized ubiquitinated Gcn4p. These results suggest that Rpn10p is the receptor that binds the pollyubiquitin chain during ubiquitin-dependent proteolysis of Gcn4p.