väike, väga konserveerunud valk, mis esineb kõigis eukarüootide rakkudes ning seostub kovalentselt teistes valkudes oleva lüsiiniga, Very conserverd protein in all eukaryotes. Ubiquitination can affect proteins in many ways: it can signal for their degradation via the proteasome, alter their cellular location, affect their activity, and promote or prevent protein interactions.