Sequence determinants of DNA bending in the ilvlH promoter and regulatory region of Escherichia coli.

Previous studies have shown that the promoter/regulatory region of the ilvlH operon displays intrinsic curvature, with the bend center located at position -120 relative to the transcription start site. In this report, a 57 bp sequence spanning the bend center was mutagenized in vitro in order to study the relationship between nucleotide sequence and curvature measured by electrophoresis. The strategy used for analyzing the results consisted of determining the strengths of the relationships between electrophoretic anomaly and predicted curvature calculated by computer programs that differ in wedge angle composition. The results revealed that programs which assume that bending occurs only at AA/TT display good predictive value, with correlation coefficients between electrophoretic anomaly and predicted curvature as high as 0.93. In contrast, a program which assumes that bending occurs at all 16 dinucleotide steps exhibited lower predictive value, while there were no significant relationships between the experimental data and curvature calculated by a program that was based on all non-AA/TT wedge values. These results show that the complete wedge model which incorporates values for all dinucleotide steps does not adequately describe the electrophoretic data in this report.