Before revision:  Here we consider the simplest unit of gene regulation ,  the repressed gene, which is instead characterized by nonlinear dependencies on external parameters , leading to corresponding nonlinear extrinsic noise.
After revision:  In biology, the Gaussian approximation has been successful in specific systems, but the relevant noise being usually non-Gaussian , the repressed gene, which is instead characterized by nonlinear dependencies on external parameters , leading to corresponding nonlinear extrinsic noise.