Technique for production of three dimensional images from electron micrographs.

 An electron micrograph is scanned into a computer (1) and images of individual particles are selected (2).  A computer algorithm , the "Common Lines", is analyses the selected image to determine the orientation of the particle relative to the incident beam of electrons.  All particles having identicle orientations are placed into a single data set and the images are averaged together.  A Fourier transform of each uniquly orientated data set is produced (3).  The various Fourier transforms are combined (4) and a transform of this combined data set (5) renders a three dimensional image of the virus particle (6).

The common lines algorithm operates only on virus particles which are icosahedral in symmetry. It can not be used to determine the structure of virus which do not have this basic structure.  Most membrane containing viruses do not have this rigid symmetrical structure. Sindbis virus has icosahedral symmetry and is one of the only membrane viruses for which an accurate three dimensional structure determined at high resolution is possible

Image provided by Dr. Angel Parades, Baylor College of Medicine