Question

A series of λ mutations that disrupt the ability of the phage to complete its life cycle have been isolated. If there is mutation in the crossover region within the attP site, the following will happen:

	A.	No insertion or duplication
	B.	No insertion
	C.	No insertion or excision
	D.	No excision

Answer 1

The integration of phage occurs at a site of attachment(att) on both phage ad bacterial genomes. The complementary sequence in circular phage genome is called attP. Integration is process of sequential exchange or genetic recombination through holiday junction and requires phage protein called Int and bacterial protein called integration host factor (IHF). Both these proteins should bind at attP. Therefore, a mutation in attP does not allow the phage and bacterial proteins to bind and thus prevent the insertion of phage into host. Option B is correct.