A virus that infects a hyperthermophile encapsidates A-form DNA

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Science  22 May 2015:
Vol. 348, Issue 6237, pp. 914-917
DOI: 10.1126/science.aaa4181

A viral DNA form that survives extremes

The prokaryote Sulfolobus islandicus lives at extreme temperatures (∼80°C) and acidity (pH 3). It is infected by the rudivirus SIRV2. DiMaio et al. determined the structure of the SIRV2 virus using cryo–electron microscopy to understand how the virus survives these brutal conditions. Most DNA in nature assumes a B-form shape. The virion, on the other hand, contains highly unusual A-form DNA that may help it survive adverse conditions. The viral capsid protein forms an extended α-helical structure that wraps around the viral DNA, possibly stabilizing the A-form DNA.

Science, this issue p. 914


Extremophiles, microorganisms thriving in extreme environmental conditions, must have proteins and nucleic acids that are stable at extremes of temperature and pH. The nonenveloped, rod-shaped virus SIRV2 (Sulfolobus islandicus rod-shaped virus 2) infects the hyperthermophilic acidophile Sulfolobus islandicus, which lives at 80°C and pH 3. We have used cryo–electron microscopy to generate a three-dimensional reconstruction of the SIRV2 virion at ~4 angstrom resolution, which revealed a previously unknown form of virion organization. Although almost half of the capsid protein is unstructured in solution, this unstructured region folds in the virion into a single extended α helix that wraps around the DNA. The DNA is entirely in the A-form, which suggests a common mechanism with bacterial spores for protecting DNA in the most adverse environments.

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