DNA LOOPS INDUCED BY COOPERATIVE BINDING OF TRANSCRIPTIONAL ACTIVATORPROTEINS AND PREINITIATION COMPLEXES

DNA conformational changes are essential for the assembly of multiprot ein complexes that contact several DNA sequence elements, An approach based on atomic force microscopy was chosen to visualize specific prot ein-DNA interactions occurring on eukaryotic class II nuclear gene pro moters. Here we report that binding of the transcription regulatory pr otein Jun to linearized plasmid DNA containing the consensus AP-1 bind ing site upstream of a class II gene promoter leads to bending of the DNA template, This binding of Jun was found to be essential for the fo rmation of preinitiation complexes (PICs), The cooperative binding of Jun and PIC led to looping of DNA at the protein binding sites, These loops were not seen in the absence of either PICs, Jun, or the AP-I bi nding site, suggesting a direct interaction between DNA-bound Jun homo dimers and proteins bound to the core promoter, This direct visualizat ion of functional transcriptional complexes confirms the theoretical p redictions for the mode of gene regulation by trans-activating protein s.