Scientists have for the first time reconstituted a complex form of RNA virus from only its matching DNA template. This new approach to engineering the bunyamwera virus, which has been implicated in birth defects, could provide a way to concoct vaccines against other members of the bunyavirus family, which includes hantavirus and other nasty human pathogens.
A team led by virologist Richard Elliott of the University of Glasgow in Scotland took on a big challenge: creating a segmented, negative-strand RNA virus from matching, or complementary, DNA. Such a strategy worked in 1981 with poliovirus, but this was relatively easy because simply inserting polio cDNA into cells produced infectious virus. But negative-strand viruses are harder, because they are assembled with specific viral proteins that must also be produced in a cell. Segmented negative-strand viruses are hardest of all, because their RNA is assembled in several sections from different cDNA strands.
Elliott's team created circular DNA strands called plasmids containing the cDNA for bunyamwera virus. The plasmids also contained other key DNA pieces, including a stretch involved in copying other genes. They inserted the plasmids into cells infected with a virus that makes an enzyme for building RNA strands. The cocktail worked like a charm, as the cells churned out infectious bunyamwera particles. The group describes its work in tomorrow's issue of the Proceedings of the National Academy of Sciences.
"It's really a good paper," says virologist Bernard Moss of the National Institute of Allergy and Infectious Diseases. He notes that virologists can use this method to create segmented negative-strand viruses with altered genes, which could help probe the basic biology of these viruses. And, says Moss, bunyaviruses crippled in this fashion might someday be the basis for vaccines against hantavirus and other often-fatal hemorrhagic fevers.