In some cases the same regulators X and Y regulate several Z genes of the same system. By adjusting the strength of the interactions this motif was shown to determine the temporal order of gene activation. This was demonstrated experimentally in the flagella system of ''[[Escherichia coli|E. coli]]''.<ref name="kal2">{{cite journal |vauthors=Kalir S, McClure J, Pabbaraju K, etal |title=Ordering genes in a flagella pathway by analysis of expression kinetics from living bacteria |journal=Science |volume=292 |issue=5524 |pages=2080–3 |date=June 2001 |pmid=11408658 |doi=10.1126/science.1058758 }}</ref> | In some cases the same regulators X and Y regulate several Z genes of the same system. By adjusting the strength of the interactions this motif was shown to determine the temporal order of gene activation. This was demonstrated experimentally in the flagella system of ''[[Escherichia coli|E. coli]]''.<ref name="kal2">{{cite journal |vauthors=Kalir S, McClure J, Pabbaraju K, etal |title=Ordering genes in a flagella pathway by analysis of expression kinetics from living bacteria |journal=Science |volume=292 |issue=5524 |pages=2080–3 |date=June 2001 |pmid=11408658 |doi=10.1126/science.1058758 }}</ref> |