FACTORS WHICH INFLUENCE THE ELECTRON-MICROSCOPIC APPEARANCE OF DNA WHEN BENZYLDIMETHYLALKYLAMMONIUM CHLORIDE IS USED

When the benzyldimethylalkylammonium chloride (BAC) monolayer technique for DNA electron microscopy is used, irksome variations in the appearance of the molecules are frequently encountered. The appearance is known to be affected by the concentrations of BAC and sodium acetate. It is now shown that the relationship between these concentrations, required for producing relaxed molecules, is not unique. We demonstrate that postadsorption exposure of specimen grids to water and uranyl acetate significantly affects the extent of collapse of molecules as well as the visualization of single-stranded regions in partially denatured DNA. The prime variable influencing the appearance of the molecules is shown to be the surface properties of carbon support films. These findings facilitate establishment of suitable experimental conditions for the BAC technique as well as an appreciation of limitations on the consistency of results. © 1979 Academic Press, Inc.