Lattice supports single bilayer

The spherical membrane surrounding the poxvirus genome begins to form as an open, cup-like structure. Some have argued that the edge of the cup must be composed of two closely apposed membranes (imagine a collapsed vesicle); otherwise, the hydrophobic edges of a single membrane would be exposed to the cytoplasm. But on page 269, John Heuser confirms that poxvirus has only a single membrane bilayer. He finds that the growing membrane is stabilized by a proteinaceous lattice.Heuser imaged freeze-fractured cells infected with poxvirus. Freeze-fracturing tends to split membranes randomly along bilayer planes, thus revealing all the bilayers that are present. As only one viral membrane plane was revealed, and no known membrane is resistant to this technique, Heuser concluded that the virus has only one bilayer.

The EM images also revealed a...