Observations on the Structure of the Campinas Strain of Tobacco Rattle Virus

SUMMARY X-ray diffraction studies of oriented gels and electron microscope studies of stained sections of the campinas strain of tobacco rattle virus are described. The X-ray diffraction patterns are similar to those obtained by Finch (1965) and are interpreted in the same way. They show that the virus has a helical arrangement of protein subunits of pitch 25.5 ± 0.5 Å and that there is an integral number (3q + 1), in three turns of the helix. The cylindrically averaged diameter is 205 ± 5 Å. The electron miscroscope studies show that the particles pack together with a centre-to-centre distance of 203 ± 10 Å in the dried state. Two dark annular rings, of radii 41 ± 2 Å and 80 ± 4 Å, are seen in the transverse sections. The larger of these probably represents the radial position of the nucleic acid.