A gene trap was created by the insertion of a beta-galactosidase/neomyocin cassette and two splice acceptors into intron 5. The predicted mRNA contains exons 1 through 5. Semi-quantitative RT-PCR of gastrocnemius skeletal muscle revealed that expression of the transcript is limited to exons 1-5, and that the carboxy-terminal activation domain in exons 8-12 are not transcribed. (J:157260)