Multiple hormone-inducible enhancers as mediators of differential transcription.

Sets of genes under a common regulatory control in a given cell type are often differentially transcribed. The possibility that this differential transcription can be modulated by the number or strength of cis-acting regulatory sequences associated with a given gene was tested by using the glucocorticoid-responsive enhancer element associated with the mouse mammary tumor virus promoter. Results indicate that differential levels of hormone-inducible gene expression can be modulated in an additive way by the number of glucocorticoid-responsive enhancers associated with this promoter. Realization of these effects shows little preference for position of the additional elements with respect to the promoter. When sequences that bind the glucocorticoid receptor in vitro with somewhat lower affinity than the enhancer were tested, these additive effects were not detected. The results support that differential transcription of genes subject to a common regulatory control can be mediated, at least in part, by the number or strength of their associated cis-acting regulatory sequences.