Three-dimensional structure of unstained, frozen-hydrated extended tails of bacteriophage T4

Unsupported, unstained frozen-hydrated extended tails of bacteriophage T4 have been studied by cryo-electron microscopy. Their three-dimensional structure has been reconstructed after correlation and averaging of the information from different particles. While the reconstructions of hydrated tails show all the features found by conventional electron microscopy, they are characterized by an open structure. Individual subunits constituting the axial repeat cannot be outlined unambiguously, as the density connectivity is sensitive to the phase-contrast transfer function effects. In order to minimize these effects, we found that the best data set for three-dimensional reconstruction is composed of layer-lines corrected for the phase-contrast transfer function and an uncorrected equator.