Genetic Systems used for Removal of Marker Gene
Several transposable element systems and site-specific recombination systems are available for the removal of marker gene. These systems involve the use of transposase or recombinase enzyme, which mediates the deletion of the marker gene. The action of the enzyme is facilitated by the target sequences, which flank the marker gene. Following are two examples of many systems that are now available for removal of the marker gene. (i) Cre-loxP recombinase system involves the use of gene constructs, which will have loxP sequences (34bp) flanking the marker gene to be removed, so that when gene Cre (recombinase enzyme from bacteriophage Pl) is expressed, site (loxP) specific recombination occurs, and loxP sequences along with the marker gene will be excised and removed. (ii) In another strategy reported in the year 2000, nptllgene flanked by two 352bp phage attachment (attP)regions of lambda (l) phage is used as a marker gene (attPsequence helps λ phage in attachment to the bacterial genome).