Visualization of Unshadowed DNA by Electron Microscopy: Adsorption to a Bacitracin Film

I describe herein a simple, rapid method in which double-stranded DNAs are adsorbed with little or no distortion to a film of the oligopeptide bacitracin on a glow-discharge-activated carbon. The DNAs can be readily visualized by positive staining with uranyl acetate, which forms a smooth trace along the DNA contour against a very even background. This eliminates the need for heavy-metal shadowing, which would thicken the DNA and obscure details of the actual path traced by the DNA double helix. The stained specimen can subsequently be shadowed with tungsten if desired, however, to confirm the positioning of proteins bound to the DNA.