cDNA clones coding for the heavy c (histocompatibility antigen/B-cell Ia-like antigen/chromosome 6/men

Two cDNA clones, pDRHI and pDRH2, con- taining sequences specific for human HLA-DR antigens were iso- lated from a bank of cDNA clones made from partially purified HLA-DR mRNA from the human lymphoblastoid cell line Maja. The clones were specific for the Mr 34,000 HLA-DR antigen gly- coprotein chain. The identity of these clones was established by (i) their ability to hybridize specifically to HLA-DR mRNA in a positive selection assay; (ii) mRNA species hybridizing to the cDNA clones were expressed in B-cell but not in T-cell or fibroblast cell cultures; and (iii) a nucleotide sequence in the longer clone, pDRH2, could be translated into an amino acid sequence that is identical to the limited NH2-terminal amino acid sequence avail- able for the purified HLA-DR antigen Mr 34,000 chain. Analysis of DNA from human, mouse, and human-mouse somatic cell hy- brid lines by Southern transfer of restriction endonuclease digests indicated that the HLA-DR heavy chain is encoded in chromosome 6. This finding is compatible with the location of at least one of the HLA-D/DR heavy chain genes within the HLA region. In addi- tion, the sequences coding for HLA-DR heavy chain appear to be present in only one or a few copies in the genome and to be rel-