The Syn21 5' UTR present in PBac{LexAop2-QF2.V5.hSNAP25.HIVNES.Syx1A.Hsp70UTR} has been replaced with the canonical Drosophila Kozak sequence CAAA. As a result lexAop regulates expression of a BacTrace sensor construct beginning with the canonical Drosophila Kozak sequence, followed by QF2 fused to amino acids 141-206 from human SNAP25 (flanked by Tag:V5 at the 5' end and Tag:NES(HIV-1-Rev) at the 3' end), followed by full length Syx1A (to target the inactive sensor to the synaptic membrane) and a Hsp70 3' UTR. (GenBank MN658785.)