The Packing Structure of Crystalline RI-APC Virus

In a paper in the preceding issue of this Journal Morgan, Howe, Rose, and Moore (1) have described their studies of electron micrographs of sections of tissue infected with RI-APC viruses. The virus particle aggregates appear most frequently as well ordered two-dimensional arrays. Studies of serial sections have shown that these two-dimensional nets are planes through three-dimensional virus crystals. We have had the opportunity to examine these electron micrographs. Our study has suggested that the viral particles are packed in a cubic body-centered lattice. The determination of the probable crystal lattice structure of a virus from section micrographs cannot, for several reasons, be as certain as a determination using replica or pseudoreplica techniques (2). In the electron micrograph of a replica, the simultaneous view of two non-parallel faces which intersect along an edge may provide powerful visual evidence concerning the intermolecular packing in three dimensions. The cutting of sections, as in this study, of thickness less than the diameter of a single particle will in general produce marked distortion either in particle shape or in interparticle alignment,