<p>We intend to build a temperature-regulated genetic circuit with three different states. The transition among these states is regulated by RNA thermometers: one whose optimal temperature is 32°C and the other is 37°C. These RNA thermometers will regulate directly the transcription of two different reporter proteins (GFP and RFP) and a transcription factor (LacI). Together with a thermolabile variant of transcription factor cI, these elements are integrated so that three different states emerge in dependence to temperature changes.</p><p>Our main purpose is to provide a proof of concept for the use of RNA thermometers to regulate the expression of a transcription factor in artificial genetic circuits. We also provide guidelines for the standard characterization of other RNA thermometers and point at possible applications.</p>