New look at influenza virus.

• Position: Cryoelectron Microscopy - Brief article

New images of the influenza virus have prompted scientists to rethink previous ideas of how the virus escapes from cells, according to a study by researchers from Japan, Sweden, and the U.S.

The flu virus carries its genes in eight segments of RNA and proteins. Before escaping from a host cell, it has to assemble the right pieces and package them into a complete virus. Scientists think that shuffling these segments allows flu viruses to vary from year to year, producing new infectious strains. One theory held that the eight genetic segments are packaged randomly into viral particles, but only those with the right eight segments are viable. That would be inefficient, yet would put a natural brake on the growth rate of the virus.

The new images, taken using a technique called cryoelectron microscopy, clearly show that the eight genetic segments are organized into a precise pattern, with seven segments surrounding a central one, before the virus particle wraps itself in an outer coating and membrane and subsequently buds out of the cell.

"It was thought that viral RNA packaging...