Archaea are generally less familiar to us and less well-studied than bacteria or eukaryotes, and the same is true for their viruses. Quax et al. report that the Sulfolobus islandicus rod-shaped virus 2 (SIRV2) employs an unusual means of escaping from its hyperthermophilic host. Using structural and biochemical analyses, these authors find that a pyramidal assembly—a heptamer of the 10-kilodalton viral protein P98—forms on the cell surface of the host cell. Each face of the pyramid is an isosceles triangle, whose base is roughly 90 nm wide and whose sides are 150 nm long. In the lytic phase of viral growth, the pyramid opens like the petals on a flower (shown above) to release the new wave of virions. Remarkably, expression of P98 in the bacterium Escherichia coli was sufficient to induce the formation of similar structures protruding from the inner membrane into the periplasmic space, although only closed pyramids were observed.
source: Journal of science