DNA bending between upstream activator sequences increases transcriptional synergy.

To determine if DNA bending enhances transcriptional synergy between tandem upstream activators, we constructed a series of synthetic promoters containing either an AP1 or an NF1 site linked to four copies of the putative transcription factor binding site ACGTGA incorporated into an intrinsic DNA bending sequence. In transient transfection, the intrinsic bending sequence between AP1 and the TATA box or between NF1 and the TATA box elicited a strong synergistic activation of transcription. The synergistic activation of transcription was greatly reduced when the intrinsic bending sequence was replaced with a mutant sequence which retains the binding site, but does not bend the DNA, and when the intrinsic bending sequence was upstream of the AP1 or NF1 sites. These data indicate that bent DNA located between upstream activator sequences can facilitate transcriptional synergism between bound activators.