|MoBio||Regulation of lambda Repressor (cI)||Chapter 4|
The life cycle of λ phages is controlled by cI and Cro proteins. The λ phage will remain in the lysogenic state if cI proteins predominate, but will be transformed into the lytic cycle if Cro proteins predominate. Transcription of the two proteins is regulated by the cI protein (λ repressor) itself.
When the host DNA is damaged (e.g., under UV irradiation), the cI protein may be cleaved by certain protease promoted by the RecA protein. Cleaved cI proteins cannot bind to the operators. Thus, the Cro proteins can be produced to transform the λ phage into the lytic cycle.