The P1 plasmid has a separate origin of replication (oriL) that is activated during the lytic cycle. Replication begins by a regular bidirectional theta replication at oriL but later in the lytic phase, it switches to a rolling circle method of replication using the host recombination machinery. This results in numerous copies of the genome being present on a single linear DNA molecule called a concatemer. The end of the concatemer is cut a specific site called the pac site or packaging site. This is followed by the packing of the DNA into the heads till they are full. The rest of the concatemer that does not fit into one head is separated and the machinery begins packing this into a new head. The location of the cut is not sequence specific. Each head holds around 110kbp of DNA so there is a little more than one complete copy of the genome (~90kbp) in each head, with the ends of the strand in each head being identical. After infecting a new cell this terminal redundancy is used by the host recombination machinery to cyclize the genome if it lacks two copies of the lox locus. If two lox sites are present (one in each terminally redundant end) the cyclization is carried out by the Cre recombinase.
Once the complete virions are assembled, the host cell is lysed, releasing the viral particles.