Bent DNA in the human adenovirus type 2 E1A enhancer is an architectural element for transcription stimulation

The upstream half of the human adenovirus type 2 enhancer adopts a curved DNA structure. Most of the enhancer elements are within the curvature, suggesting that this unusual structure is linked to enhancer function. To verify this experimentally, I constructed in vitro transcription assay systems which could distinguish any effects generated by conformational changes in a DNA template. The curved DNA conformation in the enhancer clearly affected the extent of the stimulation of the E1A gene transcription: assays using the wild-type DNA template showed that the moderately curved enhancer was superior to the highly curved enhancer in transcriptional stimulation. In additional experiments, the enhancer region was substituted with a curved DNA derived from the bacteriophage λ origin of replication. Assays using this mutant revealed that this curved segment could also act as an enhancer when it had the proper conformation. Consequently, DNA conformation may play a general role in transcriptional stimulation.