The KLF4-ESRRB module as an amplifier. We consider an autocatalytic regulation of KLF4, and cooperative positive regulation from NANOG (a). Keeping [NANOG] at various pre-determined values, we obtained the steady state concentrations and promoter activity of KLF4 and ESRRB. The relationship between these values and [NANOG] is strongly non-linear, reflecting the autoregulation and cooperative binding with NANOG. The solid line represent fitted Hill curves with n=2.3±0.2 and n=6.2±0.4 for KLF4 and ESRRB, respectively (b, c). Concentrations are presented in the units of nM.