Ubiquitin
Cell Biology · Biochemistry · Molecular Biology
Say it: yoo-BIK-wih-tin
Ubiquitin is a small, highly conserved protein that cells attach to other proteins as a tag, most often to mark them for destruction.
Also: Ub
Definition
What is ubiquitin?
Ubiquitin is a small protein of 76 amino acids found in every eukaryotic cell, from yeast to humans, with nearly the same sequence in all; its name reflects how widespread it is. It works as a removable label: enzymes attach it to other proteins, and the label decides what happens to them. This tagging, called ubiquitination, is a major post-translational modification, a chemical change made to a protein after it is built.
Three kinds of enzyme work in relay. An E1 enzyme uses ATP to activate ubiquitin, an E2 enzyme carries it, and an E3 ligase recognizes the target and bonds ubiquitin to one of its lysines, a type of amino acid. Humans make more than 600 E3 ligases, each recognizing particular targets. Extra ubiquitins can be added as a chain. Chains linked through lysine 48 send the protein to the proteasome, a barrel-shaped complex that chops it into short pieces, while single tags and other chain types change where a protein goes or what it does, as in DNA repair.
By destroying proteins on schedule, ubiquitin helps drive the cell cycle and clears out damaged or misfolded proteins. Avram Hershko, Aaron Ciechanover and Irwin Rose shared the 2004 Nobel Prize in Chemistry for uncovering this system, and faults in it are linked to cancer and to Parkinson's disease.
Word parts
Where does the word “ubiquitin” come from?
- ubiqu-
- everywhereLatin ubique
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Terms that go with it
- Post-translational modificationA post-translational modification is a chemical change made to a protein after it is built on the ribosome, often altering its activity or location.
- ProteinA protein is a large molecule made of one or more chains of amino acids, folded into a specific shape that determines its job in the body.
- EnzymeAn enzyme is a biological catalyst, usually a protein, that speeds up a specific chemical reaction without being used up in the process.
- Cell cycleThe cell cycle is the ordered series of growth, DNA copying and division stages that a cell passes through to produce two daughter cells.
- EukaryoteA eukaryote is an organism whose cells keep their DNA inside a membrane-bound nucleus and contain other membrane-bound organelles.
- Gene expressionGene expression is the use of a gene's information to make a working product, usually a protein or a functional RNA molecule.
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Checked against
Written for biofideX in plain words, after checking these references:
- NCBI MeSH: Ubiquitin
- OpenStax Biology 2e, 16.6 Eukaryotic Translational and Post-translational Gene Regulation
- Wang et al., E3 Ubiquitin Ligases: Structures, Biological Functions, Diseases, and Therapy (MedComm, 2025)
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