DNA STRUCTURE AND GENE REGULATION: THE IMPORTANCE OF BEING FLEXIBLE. Zippora Shakked, Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel

To elucidate the role of DNA structure in gene-regulatory interactions, we have investigated the crystal structures of various DNA targets in their free state and compared them to their complexes with the cognate proteins. Our results and comparisons with other regulatory systems demonstrate that certain sites of the DNA are more flexible than others and can undergo significant structural changes at low energy cost. Pyrimidine-purine base-pair doublets belong to this category. Such sites can be exploited to produce a specific interface by permitting the required DNA deformation either locally as in the trp operator and the CAP regulatory element, or globally by inducing a conformational transition from one helical form to another as in the TATA-box-containing DNA. These findings may explain the abundance of such sites in DNA sequences that are involved in transcriptional control.