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Thread: Make way for the Mamavirus and its fleas..

  1. #1 Make way for the Mamavirus and its fleas.. 
    Forum Professor sunshinewarrior's Avatar
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    ... ad infinitum?

    Even viruses have viruses, according to Wired magazine - but they spelled it miniscule, not minuscule, and that irks my prescriptionist heart.


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    Interesting. That Sputnik infects amoebae infected with Mimivirus is consistent with the emerging idea that viruses may be bigger (much bigger) players in environmental systems than generally considered.

    Here is the abstract of the paper. The Global Ocean Survey is a useful metagenomic resource. It is interesting also that the majority of putative proteins in Sputnik cannot be ascribed a function.

    Viruses are obligate parasites of Eukarya, Archaea and Bacteria. Acanthamoeba polyphaga mimivirus (APMV) is the largest known virus; it grows only in amoeba and is visible under the optical microscope. Mimivirus possesses a 1,185-kilobase double-stranded linear chromosome whose coding capacity is greater than that of numerous bacteria and archaea1, 2, 3. Here we describe an icosahedral small virus, Sputnik, 50 nm in size, found associated with a new strain of APMV. Sputnik cannot multiply in Acanthamoeba castellanii but grows rapidly, after an eclipse phase, in the giant virus factory found in amoebae co-infected with APMV4. Sputnik growth is deleterious to APMV and results in the production of abortive forms and abnormal capsid assembly of the host virus. The Sputnik genome is an 18.343-kilobase circular double-stranded DNA and contains genes that are linked to viruses infecting each of the three domains of life Eukarya, Archaea and Bacteria. Of the 21 predicted protein-coding genes, eight encode proteins with detectable homologues, including three proteins apparently derived from APMV, a homologue of an archaeal virus integrase, a predicted primase–helicase, a packaging ATPase with homologues in bacteriophages and eukaryotic viruses, a distant homologue of bacterial insertion sequence transposase DNA-binding subunit, and a Zn-ribbon protein. The closest homologues of the last four of these proteins were detected in the Global Ocean Survey environmental data set, suggesting that Sputnik represents a currently unknown family of viruses. Considering its functional analogy with bacteriophages, we classify this virus as a virophage. The virophage could be a vehicle mediating lateral gene transfer between giant viruses.
    http://www.nature.com/nature/journal...ture07218.html


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    Forum Professor sunshinewarrior's Avatar
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    Thanks for that abstract. Seems more plausible this way.
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    Indeed, I had difficulty envisioning a typical virus landing on another virus and inserting its DNA, etc etc. A coinfection is much more sensible.

    What is the thinking on how viral infections and Margulis' endosymbiosis model might overlap? In both cases one microbe is becoming internal to another, and in both cases the internalised microbe benefits, in a manner of speaking. Sputnik is hypothesised here to facilitate horizontal gene transfer between viruses. It is all vaguely reminiscent of endosymbiosis. I wonder if there examples yet to be discovered, of organelles that have obvious viral qualities, or vice versa. It would be fascinating if viruses are in fact failed organelles (or organelles failed viruses).

    One example of a seeming viral quality in an organelle, is the structure of the carboxysome. However, this is thought to be an example of convergent evolution.

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