Origin of the poxviral membrane: A 50-year-old riddle

Dales and Mosbach [3] stated, “…we have examined thousands of sectioned cell profiles containing developmental stages of the virus [VACV], but have never observed any morphological continuity between the viral envelopes and any of the adjacent cellular membranes. [...]on morphological grounds alone, we assumed that the vaccinia membranes are organized de novo.” [...]there was a possibility that some yet uncharacterized poxvirus proteins enable de novo membrane assembly. In constructing an alternative model in which the viral membrane is a closed cisterna, they cited studies suggesting that (i) the poxviral membrane is composed of 2 tightly apposed membranes without free ends, (ii) the spicule coat is on the concave surface of the viral crescent rather than the convex surface, (iii) the membrane is formed from the intermediate compartment of the secretory system (ERGIC) by a wrapping process, and (iv) the “double membrane” on MVs is discarded prior to entry and the core somehow transported across the plasma membrane to enter the cytoplasm by an unknown nonfusion mechanism. [...]the saga of poxvirus membrane biogenesis continues.