A TCC to GAC change resulting in a serine to aspartate change at amino acid 75 (p.S75D) in exon 2 introduced a phospho-mimicking mutation. The targeting vector contained 9 kb of mouse Src sequence containing the 2 bp mutation, and a 3.4 kb HSV-tk-neomycin cassette flanked by a 3.2 kb duplication containing a part of the Src sequence. The selection cassette was excised by homologous recombination within the duplication at one allele. (J:279554)