UbiQ-127 (Ac-ISG15prox-Rh110MP, Figure 1) is a quenched, fluorescent substrate for ISG15 proteases based on the C-terminal domain of mouse ISG15. In general, this C-terminal ubiquitin-like domain is sufficient for recognition by ISG15 proteases (1). Cleavage of the amide bond between the C-terminal Gly and rhodamine110 moiety releases the highly fluorescent Rh110-morpholinecarbonyl (Rh110MP) (2). 

Figure 1.

Literature: (1) Basters et al. Nat Struct Mol Biol 2017, 24, 270. (2) Terentyeva et al. Bioconj Chem 2011, 22, 1932.