Targeting of the g_i2α gene in es cells with replacement and insertion vectors

Five replacement vectors (RV) and one insertion vector (IV) were constructed in which ca. 10 kb of genomic G_i2α sequence, flanked on one (IV) or both (RV) sides by a thymidine kinase (TK) marker, were disrupted by a Neo marker inserted into the Ncol site of exon 3. G418^RFIAU^R clones corresponding to ca. 4×10⁸ ES cells electroporated with replacement vectors were analyzed and revealed no targeting event. The insertion vector, however, was integrated by a single reciprocal recombination resulting in a duplication of homology (Hit step; G418^RFIAUS^S, which was lost-together with the plasmid and the TK sequences - by intrachromosomal recombination (Run step; G418^RFIAU^R). Thus, the Hit and Run strategy can be used with a selectable marker disrupting the targeted gene, giving rise to the same targeted product that would have been expected to arise from a double crossover with a replacement vector.