Exon 2 was replaced with a modified exon 2 in which nucleotide substitutions (AAG to GCG) result in the amino acid substitution of alanine for lysine at position 44 (K44A). This mutation produces a kinase inactive protein. A floxed neomycin resistance cassette was inserted downstream of the modified exon 2. Western blot analysis confirmed reduced protein expression in splenocytes. (J:188639, J:201799)