An IRES-LacZ-neo cassette with 5' and 3' homology arms of 3.5 kb and 1.8 kb was inserted into a unique BamH1 site that lies 479 nucleotides downstream of the transcriptional initiation site in exon 3. This allele is predicted to give rise to a protein truncated after approximately 154 codons and is lacking critical residues of the T box. (J:87455)