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===Incoherent type 1 FFL (I1-FFL)===

===Incoherent type 1 FFL (I1-FFL)===

The I1-FFL is a pulse generator and response accelerator. The two signal pathways of the I1-FFL act in opposite directions where one pathway activates Z and the other represses it. When the repression is complete this leads to a pulse-like dynamics. It was also demonstrated experimentally that the I1-FFL can serve as response accelerator in a way which is similar to the NAR motif. The difference is that the I1-FFL can speed-up the response of any gene and not necessarily a transcription factor gene.<ref name="man3">{{cite journal |vauthors=Mangan S, Itzkovitz S, Zaslaver A, Alon U |title=The incoherent feed-forward loop accelerates the response-time of the gal system of ''Escherichia coli'' |journal=J. Mol. Biol. |volume=356 |issue=5 |pages=1073–81 |date=March 2006 |pmid=16406067 |doi=10.1016/j.jmb.2005.12.003 |citeseerx=10.1.1.184.8360 }}</ref> An additional function was assigned to the I1-FFL network motif: it was shown both theoretically and experimentally that the I1-FFL can generate non-monotonic input function in both a synthetic <ref name="ent1">{{cite journal |vauthors=Entus R, Aufderheide B, Sauro HM |title=Design and implementation of three incoherent feed-forward motif based biological concentration sensors |journal=Syst Synth Biol |volume=1 |issue=3 |pages=119–28 |date=August 2007 |pmid=19003446 |pmc=2398716 |doi=10.1007/s11693-007-9008-6 }}</ref> and native systems.<ref name="kap1">{{cite journal |vauthors=Kaplan S, Bren A, Dekel E, Alon U |title=The incoherent feed-forward loop can generate non-monotonic input functions for genes |journal=Mol. Syst. Biol. |volume=4 |pages=203 |year=2008 |pmid=18628744 |pmc=2516365 |doi=10.1038/msb.2008.43 |issue=1}}</ref> Finally, expression units that incorporate incoherent feedforward control of the gene product provide adaptation to the amount of DNA template and can be superior to simple combinations of constitutive promoters.<ref name="ble1">{{cite journal |vauthors=Bleris L, Xie Z, Glass D, Adadey A, Sontag E, Benenson Y |title=Synthetic incoherent feedforward circuits show adaptation to the amount of their genetic template |journal=Mol. Syst. Biol. |volume=7 |pages=519|year=2011 |doi=10.1038/msb.2011.49 |issue=1 |pmid=21811230 |pmc=3202791}}</ref> Feedforward regulation displayed better adaptation than negative feedback, and circuits based on RNA interference were the most robust to variation in DNA template amounts.<ref name="ble1"/>

The I1-FFL is a pulse generator and response accelerator. The two signal pathways of the I1-FFL act in opposite directions where one pathway activates Z and the other represses it. When the repression is complete this leads to a pulse-like dynamics. It was also demonstrated experimentally that the I1-FFL can serve as response accelerator in a way which is similar to the NAR motif. The difference is that the I1-FFL can speed-up the response of any gene and not necessarily a transcription factor gene.<ref name="man3">{{cite journal |vauthors=Mangan S, Itzkovitz S, Zaslaver A, Alon U |title=The incoherent feed-forward loop accelerates the response-time of the gal system of ''Escherichia coli'' |journal=J. Mol. Biol. |volume=356 |issue=5 |pages=1073–81 |date=March 2006 |pmid=16406067 |doi=10.1016/j.jmb.2005.12.003 |citeseerx=10.1.1.184.8360 }}</ref> An additional function was assigned to the I1-FFL network motif: it was shown both theoretically and experimentally that the I1-FFL can generate non-monotonic input function in both a synthetic <ref name="ent1">{{cite journal |vauthors=Entus R, Aufderheide B, Sauro HM |title=Design and implementation of three incoherent feed-forward motif based biological concentration sensors |journal=Syst Synth Biol |volume=1 |issue=3 |pages=119–28 |date=August 2007 |pmid=19003446 |pmc=2398716 |doi=10.1007/s11693-007-9008-6 }}</ref> and native systems.<ref name="kap1">{{cite journal |vauthors=Kaplan S, Bren A, Dekel E, Alon U |title=The incoherent feed-forward loop can generate non-monotonic input functions for genes |journal=Mol. Syst. Biol. |volume=4 |pages=203 |year=2008 |pmid=18628744 |pmc=2516365 |doi=10.1038/msb.2008.43 |issue=1}}</ref> Finally, expression units that incorporate incoherent feedforward control of the gene product provide adaptation to the amount of DNA template and can be superior to simple combinations of constitutive promoters.<ref name="ble1">{{cite journal |vauthors=Bleris L, Xie Z, Glass D, Adadey A, Sontag E, Benenson Y |title=Synthetic incoherent feedforward circuits show adaptation to the amount of their genetic template |journal=Mol. Syst. Biol. |volume=7 |pages=519|year=2011 |doi=10.1038/msb.2011.49 |issue=1 |pmid=21811230 |pmc=3202791}}</ref> Feedforward regulation displayed better adaptation than negative feedback, and circuits based on RNA interference were the most robust to variation in DNA template amounts.<ref name="ble1"/>

===Multi-output FFLs===

===Multi-output FFLs===