text: An enzyme that binds to this protein forms a heterodimer with APPBP1 to modify another protein very similar to this one called NEDD8.
full_question: An enzyme that binds to this protein forms a heterodimer with APPBP1 to modify another protein very similar to this one called NEDD8. Another enzyme that binds to this protein is encoded in humans by CDC34. This protein forms thioester linkages with three different classes of enzymes with which it interacts in sequence. This protein forms an isopeptide bond between its C-terminal glycine residue and a lysine side chain on its substrate. This protein binds to namesake "activating" and "conjugating" enzymes, labeled E1 and E2, and its attachment to targets by E3 ligases directs those targets to the proteasome. For 10 points, name this small protein that gets attached to proteins targeted for degradation, which is named for the fact that it is found in almost all cells.
first_sentence: An enzyme that binds to this protein forms a heterodimer with APPBP1 to modify another protein very similar to this one called NEDD8.
raw_answer: ubiquitin