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. RNF39 (RING finger protein 39), also known as HZFW, HZF or LIRF, is a 420 amino acid protein that localizes to the cytoplasm and contains one RING-type zinc finger and one SPRY domain. Expressed in testis, RNF39 is thought to play a role in maintaining prolonged LTP (long term-potentiation, or the process by which synaptic strength continues to increases following chemical stimulation). Via its ability to influence the length of the LTP response, RNF39 functions to regulate early synaptic plasticity. Multiple isoforms of RNF39 exist due to alternative splicing events.