A virus recognizes the starting point on the DNA to be packaged inside its protein shell
The Cingolani group (Thomas Jefferson U) has now determined the structure of TerS from the Pseudomonas phage PaP3. Phage DNA to be packaged contains multiple copies of the genome, but just one copy is needed to fill a procapsid. Terminases attempt to package this one copy by various methods; in PaP3 a termination signal is provided by the interaction of a specific sequence in the DNA (the cos sequence) with TerS.