title: Evidence for an early heavy chain intermediate in the assembly of H-2Db class I MHC molecules.
abstract: Several recently proposed models for the in vivo biogenesis of class I MHC molecules focus on the retention of empty dimers as a postulated intermediate in the assembly of the complete complexes. The data presented in this study support a slightly different model of class I biogenesis, which includes a precursor population of H-2Db heavy chains (HCs) that is retained in the ER of murine cells prior to its association with beta-2 microglobulin (beta 2m). For this study the intracellular ratios of the subunits that comprise class I molecules have been manipulated to generate a transfected cell line which assembles only very small numbers of unstable H-2Db molecules. Immunoprecipitation experiments with this transfected cell line demonstrated that nascent beta 2m was assembled into complete H-2Db heterotrimers more rapidly than nascent H-2Db HCs by normal murine cells. These data were not consistent with the simultaneous retention of the two associated subunits (HC and beta 2m) in a pool of precursor molecules. However, a previously uncharacterized subset of immature H-2Db HCs, which were not associated with beta 2m, has been detected. These immature HCs exhibited several characteristics of a precursor to complete class I molecules and required a supply of endogenously synthesized peptides for their normal processing in vivo.
authors.affiliation: University of California San Diego, Department of Biology, La Jolla 92093-0063.
authors.forename: L S
authors.initials: LS
authors.lastname: Cauley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D005434:Flow Cytometry; D006183:H-2 Antigens / Q000096:biosynthesis* / Q000737:chemistry / Q000276:immunology*; D064532:Histocompatibility Antigen H-2D; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D014162:Transfection; D001613:beta 2-Microglobulin / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D006183:H-2 Antigens; D064532:Histocompatibility Antigen H-2D; D001613:beta 2-Microglobulin