Fig. 7.

The Regulation of Protein ubiquitination through Sch9 signaling during growth. A speculative model of how reduced Sch9 signaling down-regulated ubiquitinated proteins by Rim15-dependent stress-resistance pathways (left arm) and adaptive mitochondrial ROS signaling (right arm). Elevated respiration in sch9∆ cells is mediated by upregulation of the transcription factors Hap4 or Hcm1 which gives rise to increased respiration and intracellular superoxide during growth [32,33]. Superoxide may serve as an adaptive signal to activate stress response genes (horizontal arrow). Therefore, although elevated cellular superoxide leads to accumulated H₂O₂, enhanced stress Resistance via Rim15 pathway and adaptive superoxide signal [30], on the other hand, diminishes H₂O₂ more effectively (bold arrow). Elimination of H₂O₂ in sch9∆ cells in turn reduces the oxidation of intracellular proteins including those of newly synthesized and their subsequent ubiquitination.