Analysis of D2 d : a D-region class I gene

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Abstract
The mouse major histocompatibility complex is composed of several genes arranged into the K, D, Qa, and Tla regions. The D region of the BALB/c mouse includes genes D2 d , D3 d , and D4 d , in addition to H-2D d and H-2L d . We have determined the DNA sequence of the D2 d gene and compared it with the known sequences of several class I genes. The exon/intron structure of the D2 d gene is similar to other class I genes. It also contains similar 5′ regulatory elements. A frameshift occurs in exon seven, resulting in a gene product with a truncated cytoplasmic tail. To examine the surface expression of the D2d molecule, we generated an exon-shuffled construct containing the promoter and exons 1–3, encoding the signal peptide, α1, and α2 external domains of the D2 d gene linked to exons 4–8, encoding the α3, transmembrane and cytoplasmic domains, of the H-2D d gene. The construct was transfected into mouse L cells, and a protein was detected at the cell surface by a monoclonal antibody (mAb) specific for the α3 domain of H-2Dd, as well as by other class I-specific mAbs. Although D2d is expressed at low levels, it may be a functional class I gene that most probably evolved from a Qa region gene.