A single 490 bp long intracisternal A particle long terminal repeat was found at the 3' end of the gene in several inbred mouse strains. The inserted LTR sequence provides a polyadenylation signal and creates an extended 504 bp long 3' untranslated region. This allele is present in C3H, BALB/c, C57BL/6J, SJL, SWR, A/J, and AKR. The allele is absent in CBA, DBA, 129/Sv, 129/Ola, PL, M. spretus, M. castaneus, M.molossinus, M. m. musculus, and M. m. domesticus.