The gene was disrupted by the random integration of the pGT1.8TM gene trap vector into intron 4, 414 bp downstream of the 3' end of exon 4. While normal transcript was undetected, fusion transcript consisting of endogenous (exons 1 through 4) and vector sequence was detected by Northern blot analysis. Western blot analyses followed by radioimmunoassays showed a near complete ablation of protein expression (less than 1%).