A neomycin resistance cassette replaced about 2.5 kb of sequence including the entire second and third exons which encode the N-terminal portion of the CUB domain. This deletion creates a frameshift such that a truncated transcript containing nothing downstream of the signal peptide in the original frame, and only 21 amino acids downstream of the frameshift translated into the new frame. RT-PCR failed to detect wild-type transcript in mutants. Protein was not detected in mutant MEFs. (J:104148)