cDNA clones for the heavy chain of HLA-DR antigens obtained after immunopurification of polysomes by monoclonal antibody.

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Abstract
A monoclonal antibody (HC 2.1) directed against the separated H chain of human HLA-DR was prepared. By binding HC 2.1 to polysomes from human B lymphoblastoid cells followed by the use of a protein A-Sepharose column as an immunoadsorbent, the mRNA coding for the HLA-DR H chain was purified nearly to homogeneity. The immunopurified mRNA was used to prepare labeled C[complementary]DNA with which to probe cDNA libraries. Double-stranded cDNA was also made from the immunopurified mRNA and cloned directly into [plasmid] pBR322. Two clones, one from each of the above procedures, positively selected DR H chain message as assayed by cell-free translation and immunoprecipitation. One clone, pDRH-2 [500 base pairs plus 75 base pairs of poly(A)], contains the entire 3'' utranslated region as well as coding information for the carboxy-terminal hydrophilic intracellular domain and part of the hydrophobic transmembrane region. Results of carboxypeptidase digestion of the H chains from detergent-solubilized (p34) and papain-treated (p33) HLA-DR antigen were consistent with the predicted protein sequence. Specific immunopurification of polysomes by defined monoclonal antibodies followed by direct cloning of cDNA to the highly purified mRNA is a powerful method for obtaining identified cDNA clones.