In ES cells containing Rad50tm1Flv, which lacks DNaseI hypersensitive site 7 (RHS7), floxed neo cassette replaces DNaseI hypersensitive site 4 and 5 (RHS4,5) between exon 21 and exon 22. Cre mediated recombination removed the neo cassette leaving the remaining DNaseI hypersensitive site 6 (RHS6) in intron 21 and exons 22 through 24 floxed. Western blot analysis confirmed normal protein expression. (J:165055, J:196154)