The possibilities and prospects of obtaining high-resolution information (below 30 A) on biological material using the electron microscope. Some comments and reports inspired by an EMBO workshop held at Gais, Switzerland, October 1973

Commercially available electron microscopes routinely provide resolution of some 2–4 Å, as determined on the spacing of crystalline lattices of certain stable, small-molecular substances. On biological material either macromolecules or macromolecular assemblies— ‘biologically significant’ details below some 20 Å have hitherto not been observed.we consider as ‘biologically significant’ those structural details observed or contained in electronmicrographs which are consistent with, or confirmed by, other data obtained from biochemical or functional experiments or by other physical methods (optical, magnetic, electric).

A study of heavy-light atom discrimination in bright-field electron microscopy using the computer

The Z dependence of the phase angle of the complex atomic scattering amplitude can be used to separate the image due to the heavy atoms from that due to the light atoms of the object structure. The linear theory of image formation applied to a focus series of bright-field images leads to Schiske's formula for the calculation of the structure factor. A program system is described which uses this algorithm for computing both images from a set of digitized electron micrographs of a focus series of uranyl-stained DNA on a thin carbon film.