Ubiquitin (originally, ubiquitous immunopoietic polypeptide) is a small regulatory protein that has been found in almost all tissues (ubiquitously) of eukaryotic organisms. Its gene is mapped to 16p 13.3. The ubiquitin protein itself consists of 76 amino acids and has a molecular mass of about 8.5 kDa. Ubiquitin binds to proteins and labels them for destruction. It directs protein recycling and also direct proteins to other locations in the cell, where they control other protein and cell mechanisms.