Real fibre diameters from freeze-etched Pt-C replicated fibre images: A DNA study

Abstract

Not only is recognition of characteristic filament surface structure important in identifying filaments of cellular origin but so is a reliable method for accurately measuring real filament width. Although a number of methods have been reported for estimating filament diameters these replication techniques are inappropriate for resolving filament surface detail to 12Å. To investigate how Pt-C metal replication changes the thickness of single or paired tightly wrapped hydrated DNA double helices, we have measured fibres with their long axis oriented (±5°) in the direction of metal replication in freeze-etched preparations. These fibres are coated with metal on both sides of their upper surface and are suspended horizontally above the ice surface over unshadowed regions so that both fibre edges are clearly delineated. The materials and methods have been described previously.