Lytic replication For the first few replication cycles, the lambda genome undergoes θ replication (circle-to-circle). This is initiated at the ori site located in the O gene. O protein binds the ori site, and P protein binds the DnaB subunit of the host replication machinery as well as binding O. This effectively commandeers the host DNA polymerase. Soon, the phage switches to a rolling circle replication similar to that used by phage M13. The DNA is nicked and the 3’ end serves as a primer. Note that this does not release single copies of the phage genome but rather one long molecule with many copies of the genome: a concatemer. These concatemers are cleaved at their cos sites as they are packaged. Packaging cannot occur from circular phage DNA, only from concatomeric DNA.
Lytic replication For the first few replication cycles the lambda genome undergoes θ replication (circle-to-circle). This is initiated at the ori site located in the O gene. O protein binds the ori site, and P protein binds the DnaB subunit, of the host replication machinery as well as binding O. This effectively commandeers the host DNA polymerase. Soon, the phage switches to a rolling circle replication similar to that used by phage M13. The DNA is nicked and the 3’ end serves as a primer. Note that this does not release single copies of the phage genome but rather one long molecule with many copies of the genome: a concatemer. These concatemers are cleaved at their cos sites as they are packaged. Packaging cannot occur from circular phage DNA, only from concatomeric DNA.