RT-PCR analysis of Trip13Gt expression (Figure 1D) revealed a low level of normally spliced transcripts in testes of homozygotes that is presumably a consequence of incomplete usage of the gene trap's splice acceptor. Western blot analysis, using a polyclonal antibody raised against a peptide encoded by exon 3, revealed multiple species in wild-type and heterozygous testes, one of which corresponds to the expected size of 48 kDa (Figure 1E). This and three other species were undetectable in homozygous mutant testes, but a reduced amount of an intense ∼38 kDa smaller band was present. It is not clear if this corresponds to TRIP13. The greatly decreased Trip13 mRNA and predicted correct-length protein in mutants indicate that the Trip13RRB047 allele is severely hypomorphic.