Ubiquitin is a 77 amino acid protein that targets proteins for degradation by the 26S proteasome. Ubiquitin-like (UBL) proteins are not directly involved in protein degradation, but appear to have many mechanistic similarities with the ubiquitin pathway. UBL5 (ubiquitin-like protein 5), also known as Beacon, is a 73 amino acid cytoplasmic protein that contains a ubiquitin-like domain, though it is shorter than ubiquitin and other UBL proteins. UBL proteins are also similar to ubiquitin in that they are enzymatically conjugated via an isopeptide bond between the C-terminal glycine carboxylate group and a lysine residue on the target protein; however, UBL5 lacks glycine residues at its C-terminus. UBL5 is ubiquitously expressed, though is found in highest levels in iris, kidney, muscle, brain, heart, liver and lymphoblast tissues. In the brain, UBL5 is expressed in vasopressin- and oxytocin-positive neurons and seems to be osmoregulated.