A targeting construct was designed to insert a floxed PGK-hygro into intron 24, and a third loxP site into intron 24d. The floxed region encompassed the CCC region and was removed by crossing with mice expressing cre recombinase in the germline. The final result was a chimeric intron composed of the upper half of intron 24 and the lower part of intron 24d. (J:122549)