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Major histocompatibility complex, class II, DR alpha
DR Illustration.PNG
Available structures
PDB Ortholog search: PDBe, RCSB
External IDs OMIM142860 MGI95900 HomoloGene7751 GeneCards: HLA-DRA Gene
RNA expression pattern
PBB GE HLA-DRA 208894 at tn.png
More reference expression data
Species Human Mouse
Entrez 3122 100504404
Ensembl ENSG00000204287 ENSMUSG00000036322
UniProt P01903 P14439
RefSeq (mRNA) NM_019111 NM_010381
RefSeq (protein) NP_061984 NP_034511
Location (UCSC) Chr 6:
32.44 – 32.45 Mb
Chr 17:
33.95 – 33.95 Mb
PubMed search [1] [2]

HLA class II histocompatibility antigen, DR alpha chain is a protein that in humans is encoded by the HLA-DRA gene.[1] HLA-DRA encodes the alpha subunit of HLA-DR. Unlike the alpha chains of other Human MHC class II molecules, the alpha subunit is practically invariable. However it can pair with, in any individual, the beta chain from 3 different DR beta loci, DRB1, and two of any DRB3, DRB4, or DRB5 alleles. Thus there is the potential that any given individual can form 4 different HLA-DR isoforms (2 alleles of DRB1 and two alleles from DRB3, DRB4 or DRB5).


The polypeptide subunit encoded by this gene belongs to the HLA class II alpha chain paralogues. The class II protein is a heterodimer consisting of an alpha (DRα) and a beta chain (DRβ), both anchored in the membrane. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. Class II molecules are expressed in antigen presenting cells (APC: B lymphocytes, dendritic cells, macrophages).[1]

Gene structure and polymorphisms[edit]

The alpha chain is approximately 33-35 kDa and its gene contains 5 exons. Exon 1 encodes the leader peptide, exons 2 and 3 encode the two extracellular domains, and exon 4 encodes the transmembrane domain and the cytoplasmic tail. DRA does not have polymorphisms in the peptide binding part and acts as the sole alpha chain for DRB1, DRB3, DRB4 and DRB5.[1]


There are two different HLA-DRA chains in the human population coded by three different DRA alleles:


See also[edit]


Further reading[edit]