Duplex destabilization in superhelical DNA is predicted to occur at specific transcriptional regulatory regions

Analytic methods that accurately calculate the extent of duplex destabilization induced in each base-pair of a DNA molecule by superhelical stresses are used to analyze several genomic DNA sequences. Sites predicted to be susceptible to stress-induced duplex destabilization (SIDD) are found to be closely associated with specific transcriptional regulatory regions. Operators within the promoters of SOS-regulated Escherichia coli genes are destabilized by superhelical stresses, whereas closely related sequences present elsewhere on that genome are not. Analysis of genomic sequences from the budding yeast Saccharomyces cerevisiae finds a distinctive tripartite pattern, in which the 3' and 5' termini of genes are destabilized, but the sequence encoding the primary transcript is not. Three rDNA genes from higher eukaryotes exhibit a similar pattern. Implications of these results regarding possible mechanisms of activity of the regions involved are discussed. A strategy is presented for designing experiments in which the susceptibility to SIDD of a local region is altered without changing its local base sequence. The occurrence of the observed SIDD patterns provides a new approach to searching uncharacterized genomic sequences for transcriptionally active regions.