The amino acid sequence and gene organization of the heavy chain of the HLA-DR antigen: homology to immunoglobulins.

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Abstract
The amino acid sequence of the H chain of HLA-DR antigens was elucidated from the analysis of a genomic clone coding for this protein. A 3.2-kilobase EcoRI fragment includes 4 exons containing 227 amino acids out of 229 in the mature HLA-DR H chain. One exon (.alpha.2) encodes a domain of 94 amino acids with strong sequence homology both to Ig constant region domains and to Ig-like domains in HLA-B7, .beta.2-microglobulin and the HLA-DR light chain. A structure for the HLA-DR antigen heterodimer consisting of 4 extracellular domains, 2 of which are Ig-like [1 in the H chain (.alpha.2) and 1 in the L chain (.beta.2)] is supported. The 3rd is the amino-terminal polymorphic domain in the L chain (.beta.1) and the 4th is an invariant domain in the H chain (.alpha.1).