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Cryo-ET and Sub-tomogram averaging

Cryo-tomography is used to examine samples ranging in size from cells to large complexes. It often focuses on one-of-a-kind objects that are not amenable to averaging methodologies used in single particle EM. Structures determined using tomography can vary from low to mid resolutions (20-50 Å).

While these volumes lack detailed molecular information, one has the ability to visualize objects in the context of an intact cell at higher resolutions than what can be achieved using light microscopy. This visualization has made tomography an important technique used by cell biologists. However, in cases where multiple copies of a complex or a repeating assembly are found in a tomogram, subtomographic averaging approaches can be used. As such, it is possible to determine ~20-10 Å resolution structures.