The virus takes the form of a roughly spherical particle, approximately 0.6 μm long, containing a genome of approximately 650,000 base pairs coding for more than 500 proteins. Most of these proteins bear no resemblance to those of its Siberian predecessor, Pithovirus sibericum. Furthermore, unlike Pithovirus, which only requires the cytoplasmic resources of its cellular host to multiply, Mollivirus sibericum uses the cell nucleus to replicate in the amoeba, which makes it as host-dependent as most “small” viruses. This strategy, and other specific traits, such as a deficiency in certain key enzymes that allow synthesis of its DNA building blocks, mean that Mollivirus sibericum is more similar to the common viral types, including human pathogens such as Adenovirus, Papillomavirus, or Herpesvirus. Pithovirus, on the other hand, replicates in the cytoplasm in the same way as Poxvirus, a family that counts the now officially eradicated smallpox virus. In terms of its shape, mode of replication and metabolism, Mollivirus sibericum thus represents a new type of virus never previously observed and distinct from the three giant virus families discovered to date.
Note: What does “officially eradicated” mean in the paragraph above, as opposed to what happened to T. Rex?
This discovery, which suggests that giant viruses are not so rare and are highly diversified, also proves that the ability of viruses to survive in the permafrost for very long periods is not restricted to a particular viral type, but probably covers viral families with varied — and hence potentially pathogenic — replication strategies. More.
See also: Devolution: Getting back to the simple life
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