Discussion
Entry of λ phage lysogen to lytic phase is triggered by
Answer: B
Induction is triggered by loss of co-operativity in binding of \(\lambda\) repressor.
DNA damage activates RecA, which acts as a co-protease and stimulates the cI repressor to cleave itself between its N-terminal DNA-binding domain and C-terminal dimerisation domain. The DNA-binding fragments can no longer dimerise or bind co-operatively to the operators OR and OL, so they fall off, the lytic promoters fire, and the prophage enters the lytic cycle.
An increase in repressor would strengthen lysogeny, not end it. A decrease in RecA function prevents induction. A mutation in the phage genome is not the normal trigger.
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