The UBX domain shares the same superfold (1), and an evolutionary relationship with ubiquitin (2), and is found in ubiquitin-regulatory proteins, which are members of the ubiquitination pathway. The UBX domain is a widespread ubiquitin-like module. The function of the UBX domain is not known although the fragment of avian FAF-1 containing the UBX domain causes apoptosis of transfected cells.

1. http://pfam.xfam.org/family/PF00789

2. Buchberger A, Howard MJ, Proctor M, Bycroft M. (2001). The UBX domain: a widespread ubiquitin-like module. J Mol Biol., 307(1):17-24. PMID:11243799