Exons 4 through 6 were replaced with a neomycin selection cassette. Northern blot analysis of MEF cell lines derived from heterozygous mutant mice showed that aberrant transcripts were produced from the targeted allele. RT-PCR and sequencing analysis of the these transcripts identified chimeric transcripts that contained the neo gene as well as splice variants in which exon 3 joined exon 8. In either case, a premature stop codon was introduced immediately downstream of exon 3. (J:67076)