|MoBio||The Life Cycle of Lambda Phages||Chapter 1|
λ phages are commonly used in DNA cloning. They can have either lytic or lysogenic cycle, depending on the environment. In the lytic cycle, λ phages replicate rapidly and eventually cause lysis of the host cell. In the lysogenic cycle, the viral DNA circularizes and integrates into the host DNA. Then, λ phages may replicate with the host cell.
Under certain conditions (e.g., ultraviolet irradiation of cells), the λ phages may transform from the lysogenic cycle to the lytic cycle. This transformation is mainly controlled by two proteins: cI (also known as λ repressor) and Cro. Increase in cI proteins promotes the lysogenic cycle whereas increase in Cro proteins promotes the lytic cycle. The detailed mechanism is explained in Chapter 4 Section H.