 This results in "Krüppel" being expressed in a stripe in the center of the embryo’s A-P axis, where Hunchback concentration has dropped to a low enough level so that it can act as an activator, but "Knirps" is not yet present to inhibit.The "Krüppel" protein is a transcription factor, and has been shown to act as a repressor.It functions in collaboration with other gap genes and their localized protein products to regulate the expression of the primary pair rule genes – "even skipped" ("eve"), "hairy" ("h"), and "runt."