CRE-LOX P RECOMBINANT SYSTEM

25.      CRE–LOX P RECOMBINANT SYSTEM

Cre-Lox is a system that can be used to introduce gene deletions, inversions and translocations on specific target sits.
It was first discovered in the P1 bacteriophage as a mechanism of viral genome replication in its lysogenic cycle. Today it is commonly used to introduce inducible deletions.
The cre-Loxp system has been applied in a number of different ways, including the site-specific integration of transgene, the conventional inactivation and inactivation of transgene and deletion of the unwanted marker gene.
The system has two components:-
Cre recombinase    – 38 kDa enzyme.
Recognize and splits specific DNA sequences called Lox P sits.
Lox P – 34 bp long
Consist of two 13bp long flanking palindromic sequences separated by 5 bp spacer region.
A typical Lax P site is ATAACTCGTATA–NNNTANNN–TATACGAAGTTAT.
Lox P sites are illustrated as triangles.
The orientation of the Lox P sequence matters. Because it would determine whether Cre will produce a deletion, inversion or translocation.
(a)    Two Lox P sequences that go in the same would be recognized and cleaned by Cre, producing a deletion.

(b)    If the Lox P sites are oriented in the opposite directions, Cre would produce an inversion.

(c)    If the Lox P sites are located in different chromosomal loci, Cre recombination would produce a translocation.