Non-coding RNAs are crucial regulators of gene expression in prokaryotes and
eukaryotes, but it remains poorly understood how they affect the dynamics of
transcriptional networks. We analyzed the temporal characteristics of the
cyanobacterial iron stress response by mathematical modeling and quantitative
experimental analyses, and focused on the role of a recently discovered small
non-coding RNA, IsrR. We found that IsrR is responsible for a pronounced delay
in the accumulation of isiA mRNA encoding the late-phase stress protein, IsiA,
and that it ensures a rapid decline in isiA levels once external stress
triggers are removed. These kinetic properties allow the system to selectively
respond to sustained (as opposed to transient) stimuli, and thus establish a
temporal threshold, which prevents energetically costly IsiA accumulation under
short-term stress conditions. Biological information is frequently encoded in
the quantitative aspects of intracellular signals (e.g., amplitude and
duration). Our simulations reveal that competitive inhibition and regulated
degradation allow intracellular regulatory networks to efficiently discriminate
between transient and sustained inputs