A virus that infects a hyperthermophile encapsidates A-form DNA.
DiMaio, F., Yu, X., Rensen, E., Krupovic, M., Prangishvili, D., Egelman, E.H.(2015) Science 348: 914-917
- PubMed: 25999507 
- DOI: https://doi.org/10.1126/science.aaa4181
- Primary Citation of Related Structures:  
3J9X - PubMed Abstract: 
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.
Organizational Affiliation: 
Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.