(C) Southern blot analysis of SacI-digested DNA from either wild-type ES cells (E14) or targeted ES cell clones bearing the Atrx flox allele (1/F12 and 1/G11) or Cre-recombinant clones derived from these (1/F12B1F12 and 1/G11D5). The membrane was hybridised with the intron 17 probe indicated in (A). The expected bands of 6.2 (Atrx WT), 5.0 (Atrx flox), and 2.8 (Atrx Δ18Δneo) kb were observed.