Before revision: We define a measure of cooperativity for gene regulatory networks which we propose should be maximized under a demand for energy efficiency . We investigate its dependence on network size, connectivity and the fraction of repressory/activatory interactions. Next, we consider the cell-cycle regulatory network of the  yeast, Saccharomyces cerevisiae, as a case study and calculate its degree of cooperativity .
After revision: We define a measure of cooperativity for gene regulatory networks which we propose should be maximized under a demand for energy efficiency and may be selected for under evolutionary pressures. We consider two recent models of the cell-cycle regulatory network of the yeast, Saccharomyces cerevisiae, as a case study and calculate its degree of cooperativity .