ELECTROSTATIC CONTRIBUTION TO THE BENDING OF DNA

A model is derived that accounts for the short-range electrostatic con tribution to the bending of DNA molecule in solution and in complexes with proteins in terms of the non-linear Poisson-Boltzmann equation. W e defined that the short-range electrostatic interactions depend on th e changes of the polyion surface charge density under deformation, whi le the long-range interactions depend on the bending-induced changes i n distances between each two points along the polyion axis. After an a ppropriate simplification of the Poisson-Boltzmann equation, the short -range term is calculated separately giving the lower limit for the el ectrostatic contribution to the DNA persistence length. The result is compared with the theoretical approaches developed earlier [M. Fixman, J. Chem. Phys. 76 (1982) 6346; M. Le Bret, J. Chem. Phys. 76 (1982) 6 243] and with the experimental data. The conclusion is made that the r esults of Fixman-Le Bret, which took into account both types of the el ectrostatic interactions for a uniformly bent polyion, give the upper limit for the electrostatic persistence length at low ionic strength, and the actual behavior of the DNA persistence length lies between two theoretical limits. Only the short-range term is significant at moder ate-to-high ionic strength where our results coincide with the predict ions of Fixman-Le Bret. The bending of DNA on the protein surface that is accompanied by an asymmetric neutralization of the DNA charge is a lso analyzed. In this case, the electrostatic bending energy gives a s ignificant favorite contribution to the total bending energy of DNA. I mportant implications to the mechanisms of DNA-protein interactions, p articularly in the nucleosome particle, are discussed. (C) 1997 Elsevi er Science B.V.