The feedforward loop — the most over-represented 3-node transcription network motif — acts as a sign-sensitive delay and pulse generator.
In the C1 (coherent type-1) FFL, X activates Y and Z, and Y also activates Z. This implements a delay-on / sharp-off filter. The I1 (incoherent) FFL produces a pulse (pulse generator). Both appear far more often in E. coli and yeast gene networks than expected by chance (Shen-Orr et al. 2002).