Simulations of the influences of negative feedback regulation and time scale separation on noise in the intermediates of a three-level cascade.

Faster (or slower) than X indicates that the synthesis and degradation rate constants of Y and Z where 10 and 100 times higher (or lower) than those of X, respectively. For all steady states, all molecules have the same copy number, and fluxes. The sensitivities (local response coefficients) do not depend on the chosen time scales for , , and (see main text). The kinetic descriptions follow mass action, e.g. and for the synthesis and degradation of , resp., except for the synthesis of , which was modelled as . The statistics derive from at least steps in the Gillespie algorithm.