Visualization of deoxyribonucleic acid molecules by protein film adsorption and tantalum-tungsten shadowing.

Preparatory procedures and high resolution shadowing of deoxyribonucleic acid (DNA) molecules for electron microscopy are described. They involve a two-stage mounting of the DNA on cytochrome c monolayers and shadowing with tantalum-tungsten. Conditions are determined that produce a smooth substrate and reproducible binding of the DNA strands in a randomly coiled manner without obvious stretching artifacts. When limiting factors such as excess buffer salts are eliminated, the DNA strands have the over-all dimensions expected from the naked molecule.