Epistasis and pleiotropy as natural properties of transcriptional regulation (Q1914178)

A mathematical model of transcriptional regulation in early \textit{Drosophila} embryogenesis is discussed. The model describes the threshold-dependent activation of \textit{hunchback} gene transcription -- \textit{hunchback} is responsible for dividing the embryo into segmental regions -- by a protein called Bicoid. In order to analyze this genetic switch the author extends a model describing a similar switch behavior of bacterial phage lambda by \textit{G.K. Ackers} et al. [Proc. Natl. Acad. Sci. USA 79, 1129-1133 (1982)]. Model parameters include the number of binding sites for the Bicoid activator in the \textit{hunchback} promoter and DNA-protein as well as protein-protein cooperative binding energies. The model produces response curves presenting the level of gene transcription at a given activator concentration and shows that the sharpness of the threshold depends essentially on the number of binding sites.