Electron Microscopy of Protein-Nucleic Acid Complexes: Enhanced High-Resolution Shadowing

I describe herein a method in which pretreatment with low concentrations of uranyl acetate is used to increase the structural rigidity of protein-nucleic acid complexes, thereby substantially enhancing the information content of images obtained by high-resolution shadow-casting with tungsten, The visualization of three-dimensional objects by heavy-metal shadowcasting is along-established technique in electron microscopy (1 ), and it has long been realized that the highest resolution could be achieved by using carbon-metal mixtures or high-melting-point metals for the evaporation (2 ,3 ). Double-stranded DNAs, 2 nm in diameter, are readily visualized by high-resolution shadowing with tungsten (4 ).