In 1987, Guo discovered this "transporting" RNA species and provided the first evidence that RNA played a role in packaging DNA in Phi 29. This new type of RNA was dubbed "pRNA" for "packaging" RNA. Subsequent reports by Guo and others have since established the presence and molecular structure of pRNA.
In his latest study, Guo shows how the structure of pRNA allows the molecules to interlock in hexagon formation, and how the hexagon functions to drive DNA through its portal in a manner similar to a bolt and a screw.
"The RNA hexagon is like a bolt that is embedded in the five-sided shell of the virus, and DNA is helical, like a screw," Guo says. "Because DNA is helical, like a screw, we envision it twisting and turning through the RNA portal, and such a five-fold/six-fold mismatch would facilitate the rotation."
Guo speculates that the force that drives this action likely comes from the contraction and relaxation of the six RNA molecules, which "fire" in a sequential manner, similar to a six-cylinder car engine.
"Some evidence for such a theory has been reported," he says.
Instead of gasoline, the DNA packaging machine uses ATP, a compound vital to producing energy processes in all living cells, to provide energy for its motor, Guo says.
"ATP provides energy to condense the lengthy DNA into the limited space inside procapsids with remarkable velocity," he says.
Though Phi 29 is the first virus reported to use RNA as a motor, other related bacterial viruses have been reported to contain pRNA, says Guo. In addition, he speculates that some RNAs may perform a similar function in animal or human cells.