Existing methods to systematically characterize sequence-intrinsic activity of promoters are limited by relatively low throughput and the length of sequences that could be tested. Here we present Survey of Regulatory Elements (SuRE), a method to assay more than a billion DNA fragments in parallel for their ability to drive transcription autonomously. In SuRE, a plasmid library is constructed of random genomic fragments upstream of a barcode and decoded by paired-end sequencing. This library is transfected into cells and transcribed barcodes are quantified in the RNA by high-throughput sequencing. By computationally analyzing the resulting data using generalized linear models, we succeed in delineating subregions within promoters that are re...