This hypomorphic allele was shown to contain a 5442 bp early retrotransponson in intron 3 by PCR analysis. The transposon was similar to a known retrotransposon, MMY17106, containing 317 bp long terminal repeats followed by 6 bp target duplication sequences at each end. RT-PCR analysis of homozygous mutant mice has shown several species of aberrant transcripts and indicated that the amount of message present in homozygous mutant mice is approximately 20% of the wild-type level. (J:18650, J:53808, J:82981)