A virus that infects a hyperthermophile encapsidates A-form DNA
Frank DiMaio,1* Xiong Yu,2* Elena Rensen,3 Mart Krupovic,3
David Prangishvili,3† Edward H. Egelman2†
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 a 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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