A structure of the herpes virus capsid reveals atomic-level details for the first time thanks to cryo-electron microscopy. A team led by Hong Zhou at the University of California, Los Angeles, focused in on the biggest of all herpes pathogens, human cytomegalovirus, whose 1300-Å-diameter capsid features some 4000 proteins (Science, 2017, DOI: 10.1126/science.aam6892). Human cytomegalovirus is responsible for birth defects, organ transplant infections, and AIDS deaths. Its 235-kilobase DNA genome is more than 50% larger than that of the cold sore–causing herpes simplex virus 1. Packing in all that DNA produces tens of atmospheres of pressure that the capsid architecture must withstand. For example, a chassis protein forms a net-like layer surrounding the capsid, thereby increasing structural stability. “Our structure should inform rational design of countermeasures against human cytomegalovirus, other herpes viruses, and even HIV/AIDS,” the researchers note.