A targeting construct was designed such that nucleotides 14-114 of exon 2, encoding codons 1-33, were replaced with a human CD2 reporter cDNA and a loxP-flanked neomycin resistance gene in reverse orientation. Three copies of the SV40 poly A signal were inserted into exon 3. The first downstream in-frame methionine was at codon 119, distal to the poxvirus and zinc finger domain. Northern blot of mutant lung samples revealed a truncated transcript of 0.53 kb, and that the inserted sequence altered the normal splicing of the transcript. (J:99818)