A method of temperate phage reproduction in which the phage genome is integrated into the host chromosome as a prophage and replicates in synchrony with the host chromosome. Under special circumstances (e.g., when growth conditions for the host are poor), the phage may leave the host chromosome (deintegration or excision) and enter the vegetative state or the lytic cycle that produces progeny phage. In lambda (λ) bacteriophage (q.v.), the OR region of the genome acts as a genetic switch between the lytic and lysogenic life cycles. OR contains operator sites for C 1 and cro genes, which encode the lambda repressor (q.v.) and the cro repressor (q.v.), respectively. At any given time the developmental pathway followed by the virus depends on the relative concentrations of these repressors. See Chronology, 1950, Lwoff and Gutman; lambda phage genome.
Subjects: Genetics and Genomics.