  We show that noise-induced oscillations in a gene circuit model display
stochastic coherence, that is, a maximum in the regularity of the oscillations
as a function of noise amplitude. The effect is manifest as a system-size
effect in a purely stochastic molecular reaction description of the circuit
dynamics. We compare the molecular reaction model behavior with that predicted
by a rate equation version of the same system. In addition, we show that
commonly used reduced models that ignore fast operator reactions do not capture
the full stochastic behavior of the gene circuit. Stochastic coherence occurs
under conditions that may be physiologically relevant.
