Phage Vector

Bacteriophages

1) Viruses specifically infect bacteria.

2) Phages have simple structure: Genetic material (DNA or RNA) is encapsulated in a protective 

proteineous coat called caspid.

3) It replicates within the bacteria and lysis them.

Bacteriophage λ in Gene cloning

* It’s an E.Coli virus that can carry an insert of a range between 15-20 kb

* After Bacteriophage λ infects the E.Coli, two things may happen:

a) Lytic cycle: where the phage replicates within cell and finally lysis the cell inorder to release 100 of phage particles and this occurs in 20 minutes.

b) Lysogenic cycle: the phage DNA can be incorporated into the bacterial genome as a prophage and maintained as a benign guest through successive cell divisions.

But under environmental circumstances, the integrated phage DNA is excised out and therefore the phage enters the lytic cycle.

* The length of the Bacteriophage λ is 50kb and integration-excision (I/E) events occurs at 20 kb respectively.

* This 20 kb I/E region is replaced with 20 kb of cloned DNA.  

Bacteriophage as Vector in gene cloning