A link for unrelated viruses

Viruses which infect all three domains of life could be descended from bacteriophage | By Charles Choi

Apparently unrelated viruses that infect all three domains of life—Archaea, Bacteria, and Eukarya—could share a common ancestry, according to a report by an international team of scientists in the December 3 Molecular Cell.

So far, researchers believe they have uncovered two lineages that infect all domains, with another virus line infecting two. In the Molecular Cell study, senior author Roger Burnett, of the Wistar Institute in Philadelphia, and colleagues have now shown through molecular modeling that many of these viruses' coat protein sequences are compatible with the major coat protein of bacteriophage PRD1. That builds on earlier evidence that a number of viruses are descended from that bacteriophage. "This new experimental evidence supporting the proposed PRD1-adenovirus lineage places the idea on a much firmer footing," Burnett told The Scientist.

Viruses were often viewed and studied as unrelated families until 5 years ago, when Burnett's lab and colleagues at the University of Helsinki in Finland made the discovery by X-ray crystallography that P3, the major coat protein of bacteriophage PRD1, strikingly resembled hexon, the major coat protein of human adenovirus. Both are trimeric molecules with two viral jelly rolls, with each such barrel containing eight beta strands in tandem folded back at the middle.