UAS regulates expression of a BacTrace toxin construct (BoNT/A) in which the native receptor-binding domain (RBD) of Cbot\botA has been exchanged for a single-chain anti-GFP nanobody (VHH(GFP4)) followed by the extracellular portion of a transmembrane protein (Tag:M(rCd2)). The N-terminus has the HoneyBee Melittin signal peptide sequence for endoplasmic reticulum targeting, while the C-terminus has the Kir2.1 ER export signal to improve trafficking to the plasma membrane. TEV Tag:CS(TEVp) and thrombin cleavage sites have been introduced between the toxin light and heavy chains and between VHH(GFP4) and Tag:M(rCd2), allowing release of the toxin from the membrane after cleavage. A removable cassette is present prior to the signal peptide, comprising the B2R recombinase and Hsp70b and SV40 3' UTRs surrounded by B3RT recombination sites. Thus, B3R recombination activity can remove the cassette, placing the toxin under control of the UAS driven promoter. (GenBank MN658778.)