Figure 1.

Schematic model of lambda induction. Lambda promoters are colored in green and genes in gray. The lambda induction cascade is carried out in three stages. In the early stage, UV irradiation results in a decrease of CI levels, activating the pR and pL promoters at time t_pR , leading to the expression of the cro and N genes. During the delayed early stage, RNAP is modified so as to override transcriptional terminators, allowing the continuation of both transcripts and the expression of CII, O, P and Q. During the late stage, the Q protein modifies RNAP, initiating transcription from the pR′ late promoter at time t_pR′-tR′, to become resistant to transcription terminators present downstream, and allowing the expression of late genes that encode proteins for phage morphogenesis and host cell lysis. During the late stage of the cascade, the late gene products assemble phage virions and lyse the host at time t_lysis (Oppenheim et al, 2005).