A targeting vector was used to replace exon 4, 16 bp of intron 3, and 13 bp of intron 4 with the self-excising tACE-CRE-neo cassette. The frameshift resulting from recombination putatively results in early termination in exon 5. RT-PCR failed to detect the predicted 0.75 fragment in brain, heart, kidney, liver or muscle samples. Protein was not detected in Western blot analysis of the same tissues. (J:103742)