A nonsense mutation was introduced after codon 376 of exon 8 resulting in deletion of the C-terminal region of the protein, which includes the nuclear matrix targeting signal (NMTS), and floxed TK-neo cassette was inserted into the intron preceding exon 8. Transient expression of cre recombinase in correctly targeted cells facilitated removal of the TK-neo cassette. RT-PCR analysis and Western blot confirmed the expression of the truncated gene product in homozygous mutant animals. Sequence analysis of the RT-PCR product confirmed the presence of the premature stop codon in exon 8.