An Electron Microscope Study of the Structure of Sericesthis Iridescent Virus

Purified suspensions of Sericesthis iridescent virus were treated with a nasal decongestant, negatively stained and examined in the electron microscope. The outer icosahedral surface of the virus particles showed morphological subunits apparently in close-packed hexagonal array and 70 Å apart. The orientation of untreated particles was determined from their outline. This made it possible to measure precisely their icosahedral edge-length (860 ± 27 Å).

Prolonged storage of purified virus in distilled water at 4° resulted in disintegration of the particles into triangular, pentagonal and linear fragments. The triangles of side 700 Å were clearly composed of 55 hexagonally arrayed subunits 70 Å apart. Edges of the pentagons appeared to consist of three subunits also about 70 Å apart, while the linear fragments had a broad length distribution about a mean of 438 Å.

All these observations, interpreted by a new approach to the ‘Goldberg diagram’, suggested that the virus surface is composed of 1562 morphological subunits, though alternatives of 1292 and 1472 subunits cannot be excluded.