Mrz1, a Novel Mitochondrial Outer Membrane RING Finger Protein, is Degraded Through the Ubiquitin–Proteasome Pathway in Schizosaccharomyces pombe

The RING (Really Interesting New Gene) finger proteins are a large diverse group of Zinc finger proteins. Many determined RING finger proteins are ubiquitin-protein E3 ligases and RING E3s are the most abundant type of ubiquitin ligase. RING finger and RING finger E3s have been discovered in many organisms where they play various functions, including DNA repair, ubiquitination and mitochondrial protein quality control. In this study, we identified a novel mitochondrial protein (SPBC16G5.03) with predicted RING finger domain within an N-terminal 21–60 amino acids and named it Mrz1 (mitochondrial RING finger protein). Our results showed that Mrz1 is localized in the mitochondrial outer membrane. Deletion of mrz1 did not affect cell growth in an unstressed state, but increases sensitivity to selenite. We showed that Mrz1 was degraded during the stationary phase and blocked by addition proteasome inhibitor MG132. We further showed that the E2 enzyme Ubc13 was identified among 8 candidate proteins as the ubiquitin-conjugating enzyme in this system. These data suggested that the Mrz1 was degraded likely through the ubiquitin–proteasome system.