Structural Analysis of Macromolecular Assemblies by Electron Microscopy

The theoretical background and technical advances in instrumentation, software, and experimental methods underlying the major developments in 3D structure determination of macromolecular assemblies by EM and to review the current state of the art in the field, is presented. An early attempt to create a device to change the phase of the central beam relative to the scattered rays was done by N.Unwin, who devised a simple electrostatic phase plate that was inserted into the optical system. The representation of the object of interest is considered as faithful if the EM images corresponding to its projections are corrected for the effects of the microscope contrast transfer function (CTF). In 3D, if a known structural motif is expected to be present in the reconstructed volume, the 3D map of that motif can be used to search for occurrences of related features in the tomogram. S.D. Fuller introduced a weighting scheme to make the common lines method more effective for use with cryo EM images of icosahedral particles.