Regulation of differentiated cell-specific functions.

The demand theory of gene regulation predicts that regulated cell-specific functions in high demand (i.e., high level of gene expression frequently required) are under the influence of a positive regulatory element whereas those in low demand (i.e., high level of gene expression not frequently required) are under the influence of a negative regulatory element. Furthermore, during differentiation, when the demand regimen for cell-specific functions changes, a switch in the regulatory mechanism itself is predicted. For the case in which a function is regulated in both demand regimens, the mode of regulation will switch from positive (high demand) to negative (low demand) or vice versa. These predictions are compared with published experimental evidence and found to be in good agreement.