Icerudivirus SIRV2

SIRV2 has a linear double-stranded DNA genome. The viral DNA is replicated by 4 host DNA polymerases: Dpo1 through Dpo4. The terminal fibers mediate attachment of the virus to type 4 pili abundantly present on the host cell surface. SIRV2 is able to survive additions of 6 molar (M) urea, absolute ethanol, octanol-2, and 0.1% Triton X-100 in neutral pH and 25 degrees Celsius. SIRV2gp19 was found to be a single-stranded DNA endonuclease in 2011. This was proven by inducing a mutation in the SIRVgp19 protein Motif II from the amino acid aspartate to alanine which resulted in a loss of nuclease activity. This protein is functional within pH 7-10. Magnesium chloride was found to be a cofactor to this protein in 1971. Sodium chloride concentrations above 100 mM inhibit SIRV2gp19. == Structure ==

A three-dimensional reconstruction of the SIRV2 virion at ~4 angstrom resolution has been obtained by cryo–electron microscopy. The structure revealed a previously unknown form of virion organization, in which the alpha-helical major capsid protein of SIRV2 wraps around the DNA, making it inaccessible to solvent. The viral DNA was found to be entirely in the A-form, which suggested a common mechanism with bacterial spores for protecting DNA in the most adverse environments. == References ==