THE CYTOPLASMIC DOMAIN OF THE H-2L(D) CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX MOLECULE IS DIFFERENTIALLY ACCESSIBLE TO IMMUNOLOGICAL AND BIOCHEMICAL PROBES DURING TRANSPORT TO THE CELL-SURFACE

An antiserum was generated against a synthetic peptide corresponding t o a portion of the cytoplasmic domains of the H-2L(d) and H-2D(b) clas s I major histocompatibility complex molecules of the mouse. This anti body preparation, R4, binds exclusively to endoglycosidase H-resistant H-2L(d)/D(b) molecules which are not associated with beta2-microglobu lin. Interestingly, acquisition of resistance to endoglycosidase H pre cedes acquisition of R4 reactivity by 30 min. R4-reactive H-2L(d) and H-2D(b) molecules occur on the cell surface and are phosphorylated in vivo. Other studies show that the tyrosine in the cytoplasmic domain i s accessible to radioiodination on only a subset of H-2L(d) molecules, and that the two-dimensional electrophoretic profiles of phosphorylat ed H-2L(d)/D(b) molecules, of R4-reactive molecules, and of H-2L(d) mo lecules radiolabeled on this cytoplasmic domain tyrosine are virtually identical. R4-reactive H-2L(d) molecules do not undergo the peptide- and beta2-microglobulin-induced conformational changes characteristic of free class I major histocompatibility complex heavy chains. The acc essibility of the H-2L(d) cytoplasmic domain to R4 and to radioiodinat ion late in biosynthesis and its biological significance are discussed .