In their paper in mBio this week, Kobiler et al. explain that it's because the replication compartments herpes viruses create within an infected cell are like little private rooms: each one only contains one kind of viral genome. Using mixtures of isogenic pseudorabies viruses that express three different fluorescent proteins, the authors determined that each replication compartment probably initiates from a single incoming viral genome.
Click on the "Source: link above to read more on mBio's blog, mBiosphere.
