The Integration and Excision of the Bacteriophage Lambda Genome

Integration of the DNA of a temperate bacteriophage, such as λ, into the chromosome of an infected bacterium allows the viral genome to be replicated, even though viral functions involved in lytic development have become repressed. If repression is lifted in this lysogenized bacterium or was not established following infection, the phage DNA replicates vegetatively; the replicas are incorporated into progeny phage which are released by cell lysis. Repression without integration results in abortive lysogeny; the free nonreplicating prophage and the immunity it confers are inherited unilinearly. Normally the following two requirements for integration must be fulfilled: (1) adequate pairing between specific attachment regions on the DNA of phage and host (Zichichi and Kellenberger, 1963) and (2) an integration-specific protein specified by a viral gene (Smith and Levine, 1967; Zissler, 1967; Gingery and Echols, 1967; Franklin, 1967b; Gottesman and Yarmolinsky, 1968). If either requirement is not fulfilled, abortive lysogeny is...