Definition of "ubiquitin" []

• A small polypeptide present in the cells of all eukaryotes; it plays a part in modifying and degrading proteins (noun)

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• "Consequently, degradation of both abnormal and normal shortlived proteins was also inhibited, demonstrating that the same enzyme that is involved in ubiquitin activation for histone modification, is also involved in activation of ubiquitin for modification of substrates destined for degradation."
• "(and I believe that in several others as well) that ubiquitin was limited to eukaryotes, and its apparent presence in bacteria was due to the contamination of the bacterial extract with the yeast extract in which the bacteria were grown: growing the bacteria in a synthetic medium containing carbon (glucose) and nitrogen (ammonium chloride) sources and vitamins resulted in "disappearance" of ubiquitin from the preparation."
• "While it appeared that the term ubiquitin was not justified anymore, as it is clearly not ubiquitous, we stopped using the term APF-1 and adopted the term ubiquitin for the modifying protein in the newly discovered proteolytic system."