PRKN and Parkinson disease: Here, we focus particularly on two genetic fly models of PD, with mutations in genes that are thought to act together in a mitochondrial quality control pathway: PTEN-induced putative kinase 1 (PINK1) and the E3 ubiquitin ligase parkin. It is thought that PINK1 accumulates on the outer membrane of damaged mitochondria, where it activates parkin, leading to the ubiquitination of parkin targets on the outer mitochondrial membrane.