Figure 2.

Schematic representation of the Gal4-UAS system. In a first line, the driver line, the yeast transcriptional activation factor Gal4 is under the control of a promoter directing the expression in the tissues/cells of interest. In the other line, the responder line, the transgene of interest is expressed under the control of the upstream activation sequence (UAS). As transcription of the transgene requires the presence of Gal4, the transgene is silent in the parental responder line. When the driver line and the responder lines are crossed, the transgene is then expressed according to the Gal4 pattern.