αTub84B promoter sequences drive expression of an infection-inducible form of GAL4. The construct encodes a fusion protein consisting of the first two transmembrane helices of lbm and the complete coding region of GAL4, separated by the VP2-VP3 junction protease cleavage site of the Drosophila C virus. In the absence of infection, the lbm sequence tethers the GAL4 protein to the plasma membrane, rendering it inactive. Upon infection of the animal with Drosophila C virus, the fusion protein is cleaved by the viral protease, releasing the GAL4 protein so that in can enter the nucleus and drive transcription.