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 lambda 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.