Biosynthesis and Genetics of Ia Antigens and Their Associated Invariant Chain
Since the discovery of Ia antigens in 1974 a tremendous amount of information has been gathered on the structure, genetics and possible functions of these molecules. However, the finding in 1979 that Ia antigen immunopre- cipitates contain a third polypeptide chain, designated the Ia antigen-associated invariant chain (Ii) (1), raised new questions about the assembly, processing, and expression of Ia antigens. The Ii chain, a protein with a molecular weight of 31,000 and a pI greater than 8, is non- covalently-associated with both I-A and I-E subregioncontrolled Ia antigens (1). Recent studies have suggested that it has a rather unusual subcellular distribution. It appears to be associated with Ia chain complexes in the intracellular membranes but not in the plasma membrane (2,3) . Its carbohydrate side chains also differ from those of the α and β chains, containing mannose but not fucose (4) and lacking sialic acid (3), which suggests that the Li chain possesses only unprocessed high-mannose oligosaccharides.
KeywordsStarch Hydrate Carbohydrate Citrate Electrophoresis
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