BOVINE CONGLUTININ GENE EXON STRUCTURE REVEALS ITS EVOLUTIONARY RELATIONSHIP TO SURFACTANT PROTEIN-D

Bovine conglutinin (BC), a member of the mammalian C-type collectin su bfamily, is a serum protein synthesized in liver that is believed to p lay a role in natural host defense. Previously, we have characterized a full length BC cDNA and we now describe the partial characterization of a genomic clone that encodes for the BC gene (CGN1). BC is encoded by nine exons spanning >11 kb and has been localized previously to ba nd 18 of bovine (Bos taurus) chromosome 28. Genomic sequencing demonst rated that the signal peptide/amino-terminal domain, the carbohydrate recognition domain, and the linking peptide, a domain between the coll agenous region and the carbohydrate recognition domain, are each encod ed by a single exon. The collagenous domain is split into five exons, with the 5' most region being located within the exon that also encode s the signal peptide/amino terminus. The remaining four collagenous do main exons are tandemly arranged with lengths of 117, 108, 108, and 11 7 bp, respectively. Overall, the BC genomic organization is very simil ar to that of the human surfactant protein-D gene, SFTP4. On the basis of identical collagen domain structures, we suggest that conglutinin and bovine surfactant protein-D evolved from a gene duplication event occurring in Bovidae after divergence from other mammals.