Structure and expression of HLA-DQ alpha and -DX alpha genes: interallelic alternate splicing of the HLA-DQ alpha gene and functional splicing of the HLA-DQ alpha gene using a retroviral vector.
The nucleotide sequences of the two closely related HLA-DQ alpha and HLA-DX alpha genes have been determined. Exons coding for the signal peptide, alpha 2 and transmembrane domains are 94-99% homologous, whereas the alpha 1 exon and the promoter region have diverged as much as or more than introns and the 3' untranslated region. The promoter regions of both genes contain two short sequences thought to be important for regulation of transcription by gamma-interferon. Transfection studies established that the DQ alpha and DQ beta genes encode the HLA-DQ antigen. Transcripts of varying length are produced from different alleles as the result of the use of alternate splice and polyadenylation signals at the 3' end of the DQ alpha gene. Thus typing at the DQ alpha locus can be achieved by Northern blot analysis. No transcript of DX alpha was detected in B lymphocytes. The DX alpha gene was accurately spliced when introduced into a retroviral vector, suggesting that the lack of expression of DX alpha is not due to aberrant splice signals.