Moselio Schaechter


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« Neanderthal Me | Main | Adhering To The 'Replicon Model' The Sloppy Way »

January 30, 2014

Talmudic Question #105

Do you know of any eukaryotic virus that has a tail, and, if not, why do you suppose there aren’t any?

Comments

Would you consider the spike og Chlorellaviruses a "tail"? http://cryoem.ucsd.edu/publication-pdfs/2009-Cherrier-etal-PNAS.pdf

Merry comments: I imagine Elio had the canonical tails of the Myoviruses and Siphoviruses in mind here, in which case I'd say the spike does not qualify. Those tails are complex protein structures that are preassembled and then attached to the filled capsid where they later function as a tube for genome delivery. Like those tails, the Chlorellavirus spike indicates a unique vertex specialized for host interaction---likely your point here. Indeed the pointed spike structure may be involved in penetration of the host. However, the spike does not contain a channel for genome delivery.

'Tail' is being used to describe numerous structures even among the phages that don't conform to such a narrow definition (e.g., the extensible tail of Podophages such as T7, the protein chute formed after adsorption by PRD1, and the protein tube formed also after adsorption by phiX174). As usual, phage and virus variety confounds our terminology.

BTW, there is a more recent paper also from the Rossman lab showing that takes a close look at the Chlorellavirus spike structure during infection:
http://www.ncbi.nlm.nih.gov/pubmed/21873222

There might be some evolutionary advantage to being endocytosed by the target cell instead of requiring a tail to attach and inject genetic material. Perhaps assembly of viral tails was an evolutionary pressure that drove the first eukaryotes towards spatial arrangement of transcription and translation. Tails work for viruses like T7 phage because transcription and translation both occur in the cytosol of prokaryotes. Separation of the two processes could have been a defense against viral assembly.

Elio replies:

Nice point, Marco. Who knows, you my even be right!

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