Ubiquitin

UB

Ubiquitin is a small protein of 76 amino acids, which is highly conserved in eukaryotes and may have many roles within the cell. Covalent attachment of ubiquitin can mark a protein for proteasomal degradation.

Drosophila melanogaster ubiquitin is an N-terminal peptide, which acts as a "spacer" in the translated polypeptide and is cleaved out to separate/release the connected protein. Ubiquitin also promotes higher expression of the linked protein, likely through improving protein stability and/or folding.