Fig. 12

Physical structure, circularization, and packaging mechanism of a phage that uses headful packaging. a This figure represents the first phage chromosome packaged from a linear concatemer. The DNA inside the phage virion before infection has a similar DNA sequence at both ends. The repeat sequences at the ends of each chromosome vary from phage to phage. The bracket indicates exactly one genome-length (from one pac sequence to the next). b After infection, the ends undergo homologous recombination to form a circular DNA molecule that contains exactly one genome-length and one pac site. A linear concatemer is generated via rolling circle replication. c Beginning at the pac site, the terminase inserts the DNA into the capsid. The terminase creates imprecise cuts after slightly more than one genome length is packaged into the capsid, generating a repeated sequence at each end. Thus, the position of the pac site varies in each subsequent virion