In the A/WySnJ strain of mice, an intracisternal type A particle retrotransposon insertion occurred in exon 3, resulting in the replacememt of the final 8 amino acids of the encoded protein with 21 amino acids from the inserted element. This mutation is not present in A/J. FACS analysis indicated that an aberrant fusion protein was expressed from this allele that appeared on the cell surface; however, the protein appeared to be nonfuctional.