PJA2, also known as E3 ubiquitin-protein ligase praja-2, RNF131 (ring finger protein 131) or Neurodap1, is a 708 amino acid protein that contains one ring-type zinc finger and exists as two alternatively spliced isoforms. Significantly conserved in chimpanzee, dog, cow, mouse, rat, chicken and zebrafish, PJA2 shares 52% identity with PJA1, which is involved in protein ubiquitination in brain and may play a role in X-linked mental retardation. Encoded by a gene that maps to human chromosome 5q21.3, PJA2 localizes to both endoplasmic reticulum and Golgi apparatus membranes. Participating in E2-dependent, E3 ubiquitin-protein ligase activity, PJA2 binds to a variety of E2s and interacts with ubiquitin-conjugating enzymes, such as UBE2D2, in vitro.