UASt regulates expression of a Ubiquitin-eGFP chimera with a asparagine and a linker sequence GKLGRQ between the ubiquitin- and eGFP-coding sequences. Upon proteolytic cleavage (deubiquitination), a destabilizing amino acid (asparagine) is exposed at the N-terminus of the GFP moiety, thereby acting as an unstable GFP reporter for activity of the N-end rule pathway.