Template Matching, Alignment and Averaging of Sub-Tomograms in Electron Cryo-Tomography Reconstructions using Jsubtomo

Electron cryo-tomography has emerged as a widely used method for imaging different biological specimens and elucidating their three-dimensional structures. Suitable specimens range from macromolecular complexes, filamentous structures, coated vesicles and pleomorphic membrane viruses to procaryotic cells and thin areas eukaryotic cells. After sample preparation for electron cryo-microscopy, a tomographic tilt series is collected from the sample area of interest, from which a three-dimensional density map (a tomogram) can be calculated. Two complications limit the usefulness of these data: first, low signal-to-noise ratio, inherent to all electron cryo-microscopy data, and second, the missing wedge problem, inherent to all tomographic reconstructions with limited tilting range. However, if the tomogram contains several identical structures (particles), such as macromolecular complexes, these complications can be overcome by averaging several sub-tomograms, each containing a single particle.