The discovery of this cellular pathway arose from research on Parkinson’s disease [30,31], which revealed a particular form of recessive Parkinsonism characterized by mutation in two genes: Parkin RBR E3 Ubiquitin Protein Ligase (PARK2), which codes for a cytosolic E3 ubiquitin ligase named Parkin, and PTEN-induced kinase 1 (PINK1), whose protein product is a kinase localized on the mitochondrial surface [32,33]. The gene discussed is UBE2E3; the disease is Parkinson disease.