Phase contrast electron microscopy of viruses
Abstract: Observation of viruses by phase contrast electron microscopy which was recently developed in Japan has been performed. In this review, the results of Zernike phase contrast electron microscopy of ice-embedded influenza A virus are described in detail. Influenza A virions were 100-120 nm in diameter and consisted of core, envelope, and glycoprotein spikes. In addition to spherical and elongated virions, three other classes of virions were distinguished on the basis of the features of their viral envelope: virions with a complete matrix layer, which were the most predominant, virions with a partial matrix layer, and virions with no matrix layer under the lipid bilayer. Eight ribonucleoprotein complexes, that is, a central one surrounded by seven others, were distinguished. About 450 glycoprotein spikes were present in an average-sized spherical virion. Thus, phase contrast electron microscopy is a powerful tool for resolving the ultrastructure of viruses, because it enables the generation of high-contrast images of ice-embedded particles. It will enable 3D structural analysis of enveloped viruses at the nanometer level that was difficult to achieve by conventional electron microscopy.
Key words: Phase contrast, Transmission electron microscopy, Influenza A virus, Rapid freezing, Ribonucleoprotein complex, Glycoprotein spikes