Figure 1. Design of a genetic circuit with selected components that form a synthetic species barrier.

(A) The 5 genetic elements used: transcription factor glass, enhancer GMR, transcription factor gal4, enhancer UAS and a constitutively activated form of ras. (B,C) Arrangement of the genetic elements in two modules, a killing module (B) composed by two independent transgenes, GMR-gal4 and UAS-ras^v12,and a switch that depending on the presence or absence of the transcription factor glass can switch the killing module ON and OFF (C). (D) In the absence of Glass, activation of the killing module is not possible and the flies survive. However, in the presence of Glass, expression of the constitutively active form of ras kills the animal.