Chattm1Jrs-carring mice were crossed with transgenic mice expressing cre in the germ line to produce this allele in which exons 3 and 4 were replaced with an frt-flanked neo. Southern blot confirmed excision of the exons. RT-PCR revealed the splicing of exon 2 to exon 5, resulting in a frame shift after the codon for amino acid 22 and a stop codon at amino acid 31. Therefore, the protein products were less than 32 amino acids long, instead of the 641, and lacked the catalytic center. (J:91066)