Five evolutionarily conserved 30-bp repeated sequences in the proximal end of the transcript were deleted in a 657 bp region. A self-excising selection cassette was also placed downstream of the gene. After recombination and generation of chimeric mice, the selection cassette excised itself in the male germline leaving behind a single loxP site. Heterozygous mice that inherit the deletion paternally transcribe a truncated RNA that is missing the 657 bp of sequence but is otherwise a full length transcript.