Nucleotide Sequence of an HLA-DQ α Chain Derived from a DRw9 Cell Line: Genetic and Evolutionary Implications

Three families of human Ia molecules, DP, DQ, and DR, have previously been defined. A cDNA clone, pDSH-9.1, encoding the α chain of a DQ molecule derived from an HLA-DRw9 homozygous cell line has been isolated and sequenced. Comparison of the nucleotide and predicted protein sequence to those of other DQ α subunits reveals that DQ α subunits derived from DR4, -7, and -9 cells are very similar to each other but quite different from a DQ α subunit derived from a DRw6 cell line. These studies suggest that certain 1a haplotypes have a common evolutionary history. Furthermore, in the context of current serologic and biochemical knowledge, they suggest that the gene encoding the DQ α subunit is in strong linkage disequilibrium with the DR locus.