Cryo-ET and Sub-tomogram aveging
Cryo-tomography is used to examine samples ranging in size from cells to large complexes and 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, the ability to visualize objects in the context of an intact cell at higher resolutions than can be achieved using light microscopy 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 and it possible to determine ∼20–10 Å resolution structures.