A computer graphics study of sequence-directed bending in DNA

We present theoretical results to account for the unusual physical properties of a 423 bp DNA restriction fragment isolated from the kinetoplast of the trypanosomatid Leishmania tarentolae. This fragment has an anomalously low electrophoretic mobility in polyacrylamide gels and a rotational relaxation time smaller than that of normally-behaved control fragments of the same molecular weight. Our earlier work (Proc. Natl. Acad. Sci. USA 79, 7664, 1982) has attributed these anomalies to the highly periodic distribution of the dinucleotide ApA in the DNA sequence. As originally proposed by Trifonov and Sussman (Proc. Natl. Acad. Sci. USA 77, 3816, 1980) local features of the DNA structure such as a small bend at ApA, if repeated with the periodicity of the helix, will cause systematic bending of the molecule. Computer graphics representations of DNA chain trajectories are presented for different structural models. It is shown that the structural model of Calladine (J. Mol. Biol. 161, 343, 1982) which is based on crystallographic data, is unsuccessful in predicting the systematic bending of DNA in solution.