Abstract: RNA molecules have been shown to play a variety of functional roles in biological processes. RNA sequences can adopt 3-D conformations able to regulate transcription. RNA-based transcriptional regulators when recruited to a DNA template act to promote or suppress the transcription of nearby genes. The regulators are thought to act by mimicing the activation domains of protein transcriptional activators. These RNA-based transcriptional regulators may be engineered to regulate transcription based on the binding of a ligand such as a small molecule. RNA sequences of the regulators may be evolved to produce regulators with a greater degree of transcriptional activation or suppression. The RNA-based system of the present invention is useful in studying biological processes and in altering biological process in a therapeutic context.