Biochemical characterization of an invariant polypeptide associated with Ia antigens in human and mouse

Abstract

I i a 31,000 mol. wt polypeptide chain associated with murine and human Ia antigens was investigated for its labeling pattern, carbohydrate content and structural polymorphism. Two-dimensional gel electrophoretic analysis of tunicamycin treated cells from mouse and human lymphocytes shows that I i contains two N-linked carbohydrate chains. I i is a methionine rich polypeptide. Tryptic and chymotryptic two dimensional peptide maps of I i chain associated with I- A and I- E subregion products are identical. This absence of polymorphism holds true when I i chain is isolated from different mouse haplotypes. Human I i chains from different HLA-DR types appear also invariant by peptide map analysis. By molecular weight, carbohydrate content, charge and tryptic and chymotryptic maps criteria, I i of mouse and human are strikingly homologous.