PINK1 and PARKIN are the causal genes responsible for hereditary recessive early-onset Parkinsonism.PINK1 is a mitochondrial Ser/Thr kinase whereas Parkin is a ubiquitin-protein ligase (HECT/RING hybrid E3) that catalyzes ubiquitylation of diverse mitochondrial outer membranous proteins (Matsuda et al., JCB 2010).PINK1 and Parkin have been shown to cooperate in the recognition, labeling, and clearance of damaged (i.e., depolarized)mitochondria by selective autophagy (mitophagy).Loss of trans-membrane potential (△Ψm) causes the accumulation due to escape from △Ψm-dependent destruction and the activation via self-phosphorylation of PINK1 on depolarized mitochondria (Okatsu et al., Nat Commun 2012, JBC 2013, JCS in press).Previously we and other groups revealed that PINK1 acts as an upstream factor for Parkin, but how PINK1 activates latent Parkin and recruits cytoplasmic Parkin to damaged mitochondria are still obscure.Recently we found that PINK1 phosphorylates both Parkin and ubiquitin that are sufficient for full activation of Parkin E3 activity,and that the phosphorylated ubiquitin is a Parkin activator (Iguchi et al., JBC 2013, Koyano et al., Nature 2014).Subsequently we revealed that the phosphorylated ubiquitin chain functions as the genuine Parkin receptor for recruitment to depolarized mitochondria (Okatsu et al., JCB in press).