Exon 5 was replaced with the mouse 5' end of exon 5 including the ATG codon, human ASXL3 cDNA containing a C to G change at position 2168 (c.2168C>G) resulting in a proline to arginine substitution at amino acid 723 (p.P723R) and an FRT-flanked neomycin resistance gene. The neomycin resistance gene was removed via flp-mediated recombination. (J:322485)