The image - constructed by researchers at Rice University in the US - reveals the structure of a type of protein coat shared by hundreds of known viruses containing double-stranded RNA genomes. The image was created from hundreds of high-energy X-ray diffraction images and paints the clearest picture yet of the viruses' genome-encasing shell called a capsid.

“When these viruses invade cells, the capsids get taken inside and never completely break apart," said lead researcher Jane Tao, assistant professor of biochemistry and cell biology at Rice.

Previous studies had shown that many capsids contain dozens of copies of the capsid protein, or CP, in an interlocking arrangement. The new research identified the sphere's basic building block, a four-piece arrangement of CP molecules called a tetramer, which could also be building blocks for other viruses' protein coats. By deciphering both the arrangement and the basic building block, the research team hopes to learn more about the capsid-forming process.

"Because many viruses use this type of capsid, understanding how it forms could lead to new approaches for antiviral therapies," Tao said. "It could also aid researchers who are trying to create designer viruses and other tools that can deliver therapeutic genes into cells."

Capsids come into play because viruses can reproduce themselves only by invading a host cell and highjacking its biochemical machinery. But when they invade, viruses need to seal off their genetic payload to prevent it from being destroyed by the cell's protective mechanisms.

Though there are more than 5,000 known viruses, including whole families that are marked by wide variations in genetic payload and other characteristics, most of them use either a helical or a spherical capsid.