Electron microscopic studies of bacteriophage phi X174 intact and "eclipsing' particles, and the genome by the staining, and shadowing method.

Bacteriophage phi X174 particles were observed with a new method, a combination of staining and shadowing. Previously we used this technique to obtain clear visualization of the shape of cytoplasmic-polyhedrosis virus, especially the spikes of this particle. The phi X174 particle was observed to be an icosahedral particle of 25 nm in diameter carrying a spike at each vertex. The spike was a pentagonal frustum with a base of 9 nm and a height of 6 nm. When the phage was treated with calcium on the supporting film, the genome extruded from the particle. With the staining and shadowing method, it was clearly observed that the spike was the extruding channel of the genome. The genome extrusion occurred not only a single spike of the particle but also at two or more spikes. This implied that all 12 spikes of the particle had the same abilities to act as the channel of genome extrusion. The released genomes showed various thicknesses and shapes such as bending, looping, or branching, which were thought to reflect to compact form of DNA in a virus particle. The similarly between the spikes of bacteriophage phi X174 and those of cytoplasmic-polyhedrosis virus from silk worm was also discussed.