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A coherent feed-forward loop with a SUM input function prolongs flagella expression in Escherichia
 

Summary: A coherent feed-forward loop with a SUM input
function prolongs flagella expression in Escherichia
coli
Shiraz Kalir, Shmoolik Mangan and Uri Alon*
Department of Molecular Cell Biology and Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, Israel
* Corresponding author. Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
Tel.: 972 8 934 4448; Fax: 972 8 9344125; E-mail: urialon@weizmann.ac.il
Received 17.1.05; accepted 9.3.05
Complex gene-regulation networks are made of simple recurring gene circuits called network
motifs. The functions of several network motifs have recently been studied experimentally,
including the coherent feed-forward loop (FFL) with an AND input function that acts as a sign-
sensitive delay element. Here, we study the function of the coherent FFL with a sum input function
(SUM-FFL). We analyze the dynamics of this motif by means of high-resolution expression
measurements in the flagella gene-regulation network, the system that allows Escherichia coli
to swim. In this system, the master regulator FlhDC activates a second regulator, FliA, and both
activate in an additive fashion the operons that produce the flagella motor. We find that this motif
prolongs flagella expression following deactivation of the master regulator, protecting flagella
production from transient loss of input signal. Thus, in contrast to the AND-FFL that shows a delay
following signal activation, the SUM-FFL shows delays after signal deactivation. The SUM-FFL in
this system works as theoretically predicted despite being embedded in at least two additional

  

Source: Alon, Uri - Departments of Molecular Cell Biology & Physics of Complex Systems, Weizmann Institute of Science

 

Collections: Biology and Medicine