Exon 2 was disrupted by the insertion of a neomycin selection cassette. While Northern blot analysis of LPS activated macrophages showed the absence of normal and truncated transcripts, elongated transcript containing the neo transgene was detected in homozygous mutant mice. Normal protein was undetected by Western blot analysis, and though the absence of truncated carboxy terminal peptide was not directly confirmed, assays of bone marrow derived macrophages verified a lack of protein kinase activity.