The RING-type zinc finger motif is present in a number of viral and eukaryotic proteins and is made of a conserved cysteine-rich domain that is able to bind two zinc atoms. Proteins that contain this conserved domain are generally involved in the ubiquitination pathway of protein degradation. RNF23 (RING finger protein 23), also known as tripartite motif-containing protein 39 (TRIM39) or testis-abundant finger protein, is a 518 amino acid protein belonging to the TRIM/RBCC family that is known to interact with MOAP1. Ubiquitously expressed and existing as two alternatively spliced isoforms, RNF23 is found at highest levels in spleen, testis, brain, kidney, liver, heart and skeletal muscle. RNF23 typically localizes to cytosol but shifts to mitochondria upon co-localization with MOAP1, a short-lived, pro-apoptotic protein which RNF23 prevents from becoming poly-ubiquitinated and degraded, thereby facilitating apoptosis. RNF23 contains one B box-type zinc finger, a B30.2/SPRY domain and a single RING-type zinc finger.