Identification of bovine invariant chain (Ii) gene by nucleotide sequencing

Four overlapping cDNA clones encoding the bovine invariant chain (Ii) were isolated and characterized. The bovine Ii cDNA clone, NI3 with a 1,381-bp insert, encoded a translated product of 204 amino acids. The amino acid sequences deduced from this clone revealed that the bovine Ii gene is more closely related to human Ii gene than to genes for rodents, such as mouse and rat, but lacked 10 amino acids of the 3' end of the extracellular domain comparable to those in proteins from other species. Of interest is that the class-II-associated invariant chain peptide (CLIP) segment is present in the protein encoded by NI3, and this region exhibits a high degree of overall similarity to sequences encoded by human, mouse and rat, suggesting that bovine CLIP may have the biological function of CLIP binding to MHC class II molecules. Thus, it seems likely that this cDNA clone encodes a functional product which might perform an important function in MHC class II antigen presentation, as previously established in studies in mouse and man.