A cassette containing beta-gal and neo was inserted to replace the majority of exons 2 and 3. Western blot detected a truncated protein of 45 kDa as opposed to the 55 kDa wild-type protein. The residual protein was generated by a splicing event that involved skipping the beta-gal and neo cassette. Exon 1 was spliced to exon 4 in frame in this mutant allele. Amino acids Leu20 to Met100 were deleted, including crucial structural elements of the protein and the C-terminal half of the putative bipartite nuclear localization sequence, rendering it functionally inactive.