Gene targeting by a vector with hairpin-shaped oligonucleotide caps.

To improve the efficiency of gene targeting, a linearized vector containing part of the mouse transthyretin (ttr) gene, a bacterial neomycin-resistance gene and a herpes simplex virus thymidine kinase gene was capped with hairpin-shaped oligonucleotides. The capped vector not only improved the efficiency of positive-negative selection about 3.5-fold, but also increased about 2.5-fold the ratio of ttr gene targeted clones to the selectants.