Achieving better-than-3-Å resolution by single-particle cryo-EM at 200 keV

Nearly all single-particle cryo-EM structures resolved to better than 4-angstrom resolution have been determined using 300-keV transmission electron microscopes (TEM s). We demonstrate that it is possible to obtain reconstructions of macromolecular complexes of different sizes to better than 3-angstrom resolution using a 200-keV TEM. These structures are of sufficient quality to unambiguously assign amino acid rotameric conformations and identify ordered water molecules.