Transcriptional Control in Drosophila

We present a new model of transcriptional control. A central goal of this model is to show how modular enhancers arise from groups of binding sites. The model has a three-layer organization. The first layer describes the binding of activators and repressors to the regulatory region of a gene and incorporates the effects of repression by competition and quenching. The second layer describes adapter molecules binding to DNA-bound activators, and incorporates the effect of direct repression. Finally, the activation of transcription is modeled by an Arrhenius mechanism in which activating adapters lower the activation energy barrier. We show that this model is testable against transcription data derived from early Drosophila embryos. We believe this model is sufficiently refined to give a realistic account of the physiological consequences of complex interactions of regulatory molecules. The present approach supplements and supports, in an essential way, the insights into multigenic regulation derived from work aimed at formulating logical design principles for regulatory networks.