THE MORPHOLOGY OF DUPLEX AND QUADRUPLEX DNA ON MICA

Atomic force and low current scanning tunneling microscopy characteriz ation of duplex and quadruplex DNA (''G-wire'') morphology adsorbed on to mica reveals very different topography. This observation contradic ts similar dimensions for the two molecules as determined by spectrosc opic techniques. In the work presented here, the diameter of duplex DN A, as measured by height above the mica background, was 25% of that ob served by x-ray crystallographic methods. However, the G-wire diameter was similar to that determined by nuclear magnetic resonance and crys tallographic methods. These observations appear to be independent of t he residual buffer or scanning probe microscopy (SPM) technique used. The SPM observed widths of these molecules are similar and supports a model in which duplex DNA is pinned flat to the mica substrate. These morphological differences may be related to the variations in intermol ecular forces with the mica substrate and intramolecular forces holdin g the polymers together. (C) 1998 American Vacuum Society.