Parameter conditions for observing transitions between less-than-additive and greater-than-additive responses.

<p>Less-than-additive and greater-than-additive effects are caused by three-body-interactions between RNA polymerase and two transcription factor molecules of the same type bound at two different promoter sites. Two-body-interactions between the two transcription factor molecules are assumed to be negligible. The function is shown (solid line). The dashed line indicates the asymptote of the solid line.