Proteasomes are very large protein complexes inside all eukaryotes and archaea, as well as in some bacteria. In eukaryotes, they are located in the nucleus and the cytoplasm. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that carry out such reactions are called proteases. Proteasomes are part of a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. Proteins are tagged for degradation with a considerably small protein called ubiquitin. The tagging reaction is catalyzed by enzymes called ubiquitin ligases. Once a protein is tagged with a single ubiquitin molecule, this is a signal to other ligases to attach additional ubiquitin molecules. The result is a polyubiquitin chain that is bound by the proteasome, allowing it to degrade the tagged protein. The proteasomal degradation pathway is essential for many cellular processes, including the cell cycle, the regulation of gene expression, and responses to oxidative stress. The importance of proteolytic degradation inside cells and the role of ubiquitin in proteolytic pathways was acknowledged in the award of the 2004 Nobel Prize in Chemistry to Aaron Ciechanover, Avram Hershko and Irwin Rose.
Read the rest of this article: <http://en.wikipedia.org/wiki/Proteasome> _______________________________ Today's selected anniversaries: 1867: The Manchester Martyrs were hanged in Manchester, England, for their rescue of two Irish nationalists, who played important roles in the failed Fenian Rising, from jail. <http://en.wikipedia.org/wiki/Manchester_Martyrs> 1963: The first episode of Doctor Who was broadcast on BBC television with William Hartnell in the title role, starting a programme that eventually became the world's longest-running science fiction on television. <http://en.wikipedia.org/wiki/Doctor_Who> 1971: The People's Republic of China was given China's permanent seat on the United Nations Security Council. <http://en.wikipedia.org/wiki/China_and_the_United_Nations> 2007: MS Explorer became the first cruise ship to sink in the Antarctic Ocean. <http://en.wikipedia.org/wiki/MS_Explorer> 2009: At least 57 people, including 34 journalists, were killed in the Maguindanao massacre in the Philippines. <http://en.wikipedia.org/wiki/Maguindanao_massacre> _____________________________ Wiktionary's word of the day: gestalt (n): A collection of entities that creates a unified concept, configuration, or pattern which is greater than the sum of its parts <http://en.wiktionary.org/wiki/gestalt> ___________________________ Wikiquote quote of the day: Old wood to burn! Old wine to drink! Old friends to trust! Old authors to read! --Alfonso X of Castile <http://en.wikiquote.org/wiki/Alfonso_X_of_Castile> _______________________________________________ Wikipedia Daily Article mailing list. To unsubscribe, visit: https://lists.wikimedia.org/mailman/listinfo/daily-article-l Questions or comments? Contact [email protected]
