The DNA of bacteriophage lambda contains 48,502 nucleotide pairs forming a linear duplex. The 5′ ends of this DNA molecule have self-complementary single-stranded protrusions of 12 nucleotides that can anneal to form circles. Upon entry into the host cell, the DNA circularizes in the presence of DNA ligase. Many such circles are generated during the early lytic infection. At a later stage in replication, these individual circles/rings are converted to linear concatemers by a process called rolling-circle replication. The linear concatemers are cleaved during packaging to form monomeric chromosomal units by the enzyme DNA terminase.
