A PGK-beta-geo (beta-galactosidase-neomycin fusion gene) selection cassette was inserted into exon 4, disrupting the second ATG that gives rise to the short isoform. RT-PCR confirmed disrupted mRNA expression of the long and short forms and low expression of a miniform spanning exons 1, 6, and 7 (354 bp), which can produce a peptide from an alternative start codon in exon 7. (J:233160)