Question

Suppose there was a strain of phage λ, that had a mutated version of the cI protein that was resistant to RecA activity. Design an experiment to show that this strain cannot escape lysogeny.

Answer 1

Induction of lambda phage

you need to make three systems

1)

Infect RecA+ E.coli with wild-type lambda phage

(Acts as a control for lytic cycle induction)

2)

Infect RecA- E.coli with wild-type lambda phage

(Acts as a control for remaining of lysogenic cycle of lambda phage)

3) test system

infect RecA+ E.coli with mutant lambda phage

after infection, expose the E.coli-phage mixture solution to UV light (which activate RecA protein that inactivate cI protein). If you see plaques on plate after incubation, that indicates the phage has escaped from lysogenic cycle and if not then phage remains in lysogeny. In system 1 control you would see plaques, but in control 2 there would be no plaques as RecA is mutated.

If the result of test system is same as system 2, then you can say that this mutant lambda phage cannot escape lysogeny.