Intrinsic promoter responsiveness dictates sensitivity to transcriptional activation by enhancers

Enhancers activate specific target promoters, but whether intrinsic enhancer-promoter compatibility contributes to this specificity is debated. Recent studies using different reporter assays have reached contradictory conclusions. We compare six reporter assay designs, identify confounders that bias compatibility measurements, and apply improved assays to test 25,000 enhancer-promoter pairs. Promoters differ in their responsiveness to enhancers (>100-fold versus 1.1-fold activation) while enhancers activate all promoters in a similar rank order. Promoter output scales with enhancer activity following a power law, with the exponent varying across promoters. Incorporating this exponent into the Activity-by-Contact model improves prediction of endogenous enhancer effects, explaining why certain active genes are insensitive to distal perturbations and "skipped" by enhancers. Responsiveness is modulated by transcription factor motifs in the core promoter. This work establishes responsiveness as an intrinsic promoter property that enables specific promoters to be highly activated in a landscape of broadly compatible enhancers, while others remain unaffected.