Important cellular processes such as DNA repair, cellular differentiation, and carcinogenesis are regulated by poly(ADP-ribosyl)ation. Previously, only the nuclear protein poly(ADP-ribose) glycohydrolase (PARG) has been identified to hydrolyse poly(ADP-ribose). Poly(ADP-ribose) glycohydrolase ARH3 (ADPRHL2) is a mitochondrial matrix protein (Niere et al. 2008) structurally unrelated to PARG but possessing PARG activity (Oka et al. 2006). ADPRHL2 is able to hydrolyse poly(ADP-ribose) in mitochondria (Niere et al. 2012).