A-C) RNAP binding to 14,790 promoters from ChIP-chip data in different mouse tissues with each spot representing a single promoter. A) keratinocytes versus heart ventricles (R = +0.76). B) keratinocytes versus liver (R = +0.73). C) heart ventricle versus liver (R = +0.76). D-F) RNAP binding to the 13,861 promoters with similar RNAP binding values in heart, liver and keratinocytes.