Virus squeezed shut

The DNA in a fully packed viral capsid squeezes a pressure sensor, as revealed by images from Gabriel Lander, John Johnson (Scripps Research Institute, La Jolla, CA), and colleagues. The embrace triggers the end of DNA packaging.

Each particle of the p22 bacteriophage, a herpes cousin, contains a single copy of its genome. The DNA is pumped as a long concatamer into one end of the capsid through a portal of gp1 proteins. After one genome enters, the concatamer is cleaved and the portal plugged shut. In gp1 mutants, too much DNA is let in, but just how the wild-type portal senses full capacity was unknown.

Johnson's group viewed the fully assembled portal using automated electron microscopy, which identified items of interest systematically, thus retrieving ten...