DNA BENDING BY HEXAMETHYLENE-TETHERED AMMONIUM-IONS

DNA is bent when complexed with certain proteins, We are exploring the hypothesis that asymmetric neutralization of phosphate charges will c ause the DNA double helix to collapse toward the neutralized face. We have previously shown that DNA spontaneously bends toward one face of the double helix when it is partially substituted with neutral methylp hosphonate linkages. We have now synthesized DNA duplexes in which cat ions are tethered by hexamethylene chains near specific phosphates. El ectrophoretic phasing experiments demonstrate that tethering six ammon ium ions on one helical face causes DNA to bend by approximate to 5 de grees toward that face, in qualitative agreement with predictions. Ion pairing between tethered cations and DNA phosphates provides a new mo del for simulating the electrostatic consequences of phosphate neutral ization by proteins.