Will the Ubiquitin System Furnish as Many Drug Targets as Protein Kinases?  Philip Cohen, Marianna Tcherpakov  Cell  Volume 143, Issue 5, Pages 686-693 (November 2010) DOI: 10.1016/j.cell.2010.11.016 Copyright © 2010 Elsevier Inc. Terms and Conditions

Figure 1 Phosphorylation and Ubiquitination Regulate Most Aspects of Cell Life Phosphorylation involves the covalent attachment of phosphate to proteins, mainly to serine, threonine, and tyrosine residues. Phosphorylation is catalyzed by protein kinases and reversed by protein phosphatases. Protein ubiquitination involves the covalent attachment of ubiquitin, a small protein with 76 amino acids, to other proteins, predominantly to lysine residues. This reaction is mediated by an E1-activating enzyme, an E2-conjugating enzyme, and an E3 ligase; this reaction is reversed by deubiquitinases. Cell 2010 143, 686-693DOI: (10.1016/j.cell.2010.11.016) Copyright © 2010 Elsevier Inc. Terms and Conditions