 Tailless protein inhibits knirps gene expression in the posterior part of the embryo, allowing the knirps protein to be expressed only in the central part of the embryo (but more posterior compared to Krüppel).This is due to the ability of both hunchback and tailless to bind to the enhancer regions of knirps.The gap genes code for transcription factors that regulate the expression of pair-rule genes and homeotic genes  by competing for binding to their enhancer regions.