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. RNF17 (ring finger protein 17) or tudor domain-containing protein 4, TDRD4, SPATA23, Mmip-2 or FLJ11045, is a testis-specific protein and and novel key regulator of spermiogenesis containing 1,623 amino acids. By distributing Mad proteins to the cytoplasm, RNF17 regulates the transcriptional activity of c-Myc. Although showing localization in the nucleus, RNF17 is predominantly observed in cytoplasm and is a component of a novel nuage found in male germ cells. The gene encoding RNF17 maps to human chromosome 13q12.12 and encodes one RING-type zinc finger and four tudor domains. As a result of alternative splice events, five RNF17 isoforms exisit.