  The origin of stochastic fluctuations in gene expression has received
considerable attention recently. Fluctuations in gene expression are
particularly pronounced in cellular systems because of the small copy number of
species undergoing transitions between discrete chemical states and the small
size of biological compartments. In this paper, we propose a stochastic model
for gene expression regulation including several binding sites, considering
elementary reactions only. The model is used to investigate the role of
cooperativity on the intrinsic fluctuations of gene expression, by means of
master equation formalism. We found that the Hill coefficient and the level of
noise increases as the interaction energy between activators increases.
Additionally, we show that the model allows to distinguish between two
cooperative binding mechanisms.
