Junb^tm3Wag

A floxed and frt-flanked selection cassette containing both a neomycin resistance gene and a thymidine kinase gene was inserted in the 5' untranslated region. An additional loxP site was inserted 161 bp downstream of the translation stop codon. The neomycin and thymidine kinase genes were subsequently deleted from properly targeted ES cells by transient transfection with a flp recombinase expressing vector leaving the coding sequence flanked by loxP sites. Northern blot and Western blot analysis confirmed the absence of both transcripts and protein product. (J:88126)