Advances in High Resolution Cryo-EM Studies: the Quartenary Structure of the 70S E.Coli Ribosome Revealed at 11.5Å Resolution.

Extract

Three-dimensional cryo-electron microscopy (EM) of macromolecular assemblies with low or nonexistent symmetry in single-particle form is now recognized as a powerful, legitimate method of structure research. The progress in the resolution achieved has always been related to the introduction of new image processing methods and to improvements in understanding of the overall strategy of single particle analysis. The new techniques either were adopted from methods developed in other fields, or were specifically designed to deal with extremely low Signal-to-Noise Ratio (SNR) data in EM. In the former category we can place multivariate statistical analysis, clustering techniques, correlation techniques, and tomographic methods, in the latter alignment methods, three-dimensional (3D) projection alignment, contrast transfer function (CTF) correction methods, and common-lines based orientational search. In addition, there have been steady improvements of the quality of the data by seeking better electron microscopy conditions (usage of higher microscope voltage and of microscopes equipped with a field emission gun).