Adsorption of DNA molecules to different support films

Protein-free adsorption of the DNA of the Escherichia coli bacteriophage T7 to carbon, collodion, aluminium-beryllium and aluminium films was studied. It was found that the appearance of DNA strands depended greatly upon the kind of support film used. Direct adsorption of DNA to aluminium-beryllium or aluminium films yielded specimens with 'thin and long' and 'thick and short' regions along the strand. Well extended, uncoiled and unaggregated DNA molecules were obtained only when DNA was adsorbed to carbon, collodion or mica in the presence of intercalating dyes such as ethidium bromide. Adsorption properties of the different films are well correlated with their surface charge. Aluminium-beryllium films carry a strong positive surface charge, aluminium films a weak positive charge and carbon films a weak negative charge. It is suggested that for the preparation of specimens by spontaneous adsorption of well extended and unaggregated strands it is necessary that the DNA molecule is stiffened by a ligand such as an intercalating dye, and that the charge on the surface of the support film is opposite to the charge of the macromolecule.