A PGK-neo replaced exons 38-40, which encode the 20-residue NC3 interruption of the helical domain and one and six collagenous tripeptides located amino-and carboxyl-terminally, respectively. Sequencing of RT-PCR products confirm that the mutant transcript is in frame. Immunoblots identified a collagen-sensitive protein in mutant tissue slightly smaller than that of wild-type protein. PCR amplification indicated that mutant and wild-type transcripts are present at comparable levels in heterozygotes. (J:92510)