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The major histocompatibility complex (MHC) of the BALB/c mouse contains three genes encoding classical class I molecules, as well as at least 32 nonclassical class I genes. Although much is known about the genes encoding the classical class I molecules, the majority of the nonclassical genes have not been characterized. This report describes a newly identified nonclassical class I gene, Thy19.4, which contains an open reading frame and resembles in several regards the genes encoding classical class I molecules. The similarities include shared amino acid sequence motifs which suggest that the putative Thy19.4 molecule may assume a tertiary structure similar to that of the classical class I molecules, as well as widespread transcription in a variety of tissues. However, unlike the classical class I genes, the Thy19.4 gene maps approximately 1 cm distal to the Tla region of the MHC, in the same region as the gene encoding the Hmt element of the maternally transmitted antigen. [ABSTRACT FROM AUTHOR]

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, D3, and D4, in addition to H-2Dand H-2L. We have determined the DNA sequence of the D2gene and compared it with the known sequences of several class I genes. The exon/intron structure of the D2gene 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 D2 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 D2gene linked to exons 4-8, encoding the α3, transmembrane and cytoplasmic domains, of the H-2Dgene. 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-2D, as well as by other class I-specific mAbs. Although D2 is expressed at low levels, it may be a functional class I gene that most probably evolved from a Qa region gene. [ABSTRACT FROM AUTHOR]