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Summary: The Incoherent Feed-forward Loop Accelerates the
Response-time of the gal System of Escherichia coli
S. Mangan, S. Itzkovitz, A. Zaslaver and U. Alon*
Department of Molecular Cell
Biology and Department of
Physics of Complex Systems
Weizmann Institute of Science
Rehovot 76100, Israel
Complex gene regulation networks are made of simple recurring gene
circuits called network motifs. One of the most common network motifs is
the incoherent type-1 feed-forward loop (I1-FFL), in which a transcription
activator activates a gene directly, and also activates a repressor of the gene.
Mathematical modeling suggested that the I1-FFL can show two dynamical
features: a transient pulse of gene expression, and acceleration of the
dynamics of the target gene. It is important to experimentally study the
dynamics of this motif in living cells, to test whether it carries out these
functions even when embedded within additional interactions in the cell.
Here, we address this using a system with incoherent feed-forward loop
connectivity, the galactose (gal) system of Escherichia coli. We measured the
dynamics of this system in response to inducing signals at high temporal
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