Cell-free translation of the mRNAs for the heavy and light chains of HLA-A and HLA-B antigens.

Cell-free translation of poly(A)-containing RNA from the JY lymphoblastoid cell line followed by immunoprecipitation has indicated the presence of mRNAs for both the heavy and light chains of HLA-A and HLA-B antigens in these preparations. Both chains are synthesized with an NH2-terminal extension, approximately 20 residues in length for the light chain, and 20 or 24 residues for the heavy chains. The precursors can be processed by dog pancreatic microsomes to products similar to those obtained in vivo. Immunoprecipitation of the cell-free products has been employed as an assay for partial purification of the mRNAs. Investigation of the Daudi cell line, which cannot synthesize the small subunit, beta 2-microglobin, has indicated that the heavy chains of HLA-A and HLA-B antigens are synthesized intracellularly in vivo and can also be translated from their cognate RNAs in vitro. The implications of these findings for biosynthesis of membrane proteins in general and multimeric membrane proteins in particular, as well as the role of beta 2-microglobulin in expression of HLA-A and HLA-B antigens, are discussed.