Question

You want to use Cre/loxP system for targeted gene expression instead of knock-out. Briefly describe how this can be accomplished. (3-4 sentences)

Answer 1

Cre/loxP system for targeted gene expression

Site specific recommendation in which exchange of DNA strands takes place between segments having at least a certain degree of sequence homology.

Cre/loxp is site specific recombinase system help to carry out DNA modification by deletion, insertion,translocations and inversions at specific sites in the DNA.

To produce genetically modified organisms which have controlled gene expression, to delete undesired DNA sequences and modify chromosome architecture this tool popularly used.

Major function based on a Cre recombinase, and its recognition site, loxP adapted from the P1 bacteriophage.

Mechanism

• Two Cre proteins recognize a loxP site upon binding forms dimer.
• Then these two Cre-loxP dimers come together & form a tetramer & brings two loxP sites together with opposing directionality.
• Finally, dsDNA cleavage occurs and a crossover event occurs in center of loxP site.

Excision occurs if lox sites are in the same orientation flanking a sequence, & deleting it from its original locus.
Inversion occurs when lox sites are in opposite orientations flanking a sequence.
Translocation occurs if lox sites reside on separate parts of DNA .