UASt sequences regulate expression of a fusion protein composed of EGFP, a Tag:CS(TEVp) cleavage site and a quenching peptide. The presence of the quenching peptide (a 27 residue peptide derived from the transmembrane region of influenza M2) diminishes fluorescence of EGFP by causing its tetramerization (details from PMID:21558267). In the presence of TEVp, cleavage at the Tag:CS(TEVp) site removes the quenching peptide, increasing EGFP fluorescence.