ubiquitin

Ubiquitin is a small regulatory protein that has been found in almost all tissues of eukaryotic organisms. It directs proteins to compartments in the cell, including the proteasome which destroys and recycles proteins.

Ubiquitin can be attached to proteins and label them for destruction. Ubiquitin tags can also direct proteins to other locations in the cell, where they control other protein and cell mechanisms.

It performs its myriad functions through conjugation to a large range of target proteins. A variety of different modifications can occur. The ubiquitin protein itself consists of 76 amino acids. Key features include its C-terminal tail and the 7 lysine residues. It is highly conserved among eukaryotic species: Human and yeast ubiquitin share 96% sequence identity. The human ubiquitin sequence in one-letter code.