Abstract
Electron micrographs of flattened polyheads frequently show moire patterns of a hexagonal type. These are due to an angular displacement of the upper surface with respect to the lower, which is the necessary corollary of a helical structure of polyheads. By our observations we confirm the conclusions reached by use of another method by Finch et al. (7) in that the surface lattice of the originally tubular polyheads is of a hexagonal (P6) design. We determine the unit lattice vector to be of 67.4 ± 1.6 A. From the periodicity of the resulting moire pattern the angle formed by the upper and lower lattice can be calculated and is found to differ according to the polyhead, indicating different pitches of the helix. The circumference is constant along one individual tube but varies from polyhead to polyhead within a factor of about two. On polyheads we occasionally observe distinct morphological subunits (“capsomeres”) which appear to be segments of a hollow cylinder with an outer diameter of 70–80 A and with a hole of 20–40 A. On normal capsids of T4, capsomeres are not readily visible. Polyheads and capsids are also different with respect to buoyant densities and chemical stability.
Published Version
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