Viral interference at the level of capsid size determination by satellite phage P4

Satellite virus P4 is a defective bacteriophage which requires all 17 late morphogenic gene products of its P2 coliphage helper for normal lytic development. We demonstrate here that during this helper-satellite virus interaction the satellite P4 blocks a late step in the lytic development of the P2 helper. During co-infection, replication and processing of helper and satellite DNAs proceed normally. However, only small satellite size capsids are assembled.