Ub/Ub-like specificity assay measuring activity of WT and inactive Cys-to-Ala wMelOTU toward the Ub-, ISG15-, NEDD8-, and SUMO1-KG(TAMRA) substrates. Ub/Ub-like specificity assay measuring activity of WT and inactive Cys-to-Ala BurkOTU toward the Ub-, ISG15-, NEDD8-, and SUMO1-KG(TAMRA) substrates. Note that the rise in fluorescence polarization signal, indicative of a noncovalent interaction, is specific to the Ub substrate. 