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Class I major histocompatibility molecules (MHC) are 45 kilodalton (kD) glycoproteins that associate with a smaller 12 kD polypeptide, [beta]2-microglobulin. In the BALB/c mouse, there are three classical class I molecules, H-2K [superscript d], D [superscript d], and L [superscript d], which are expressed throughout the body and present viral antigens to cytotoxic T lymphocytes (CTLs). In addition to the genes that encode the three classical class I antigens, the BALB/c genome contains 32 genes that structurally resemble the classical class I genes, and therefore possibly encode class I molecules. A few of the non-classical class I genes have been shown to encode molecules, TL, Qa-1, Qa-2, Q10, Qb-1, and Hmt, which are expressed in a generally tissue-specific manner, and probably do not act as restriction elements. However, it is unclear what function these molecules play, or why such a large gene family is maintained if only three viral antigen-presenting restriction elements are required by the murine immune system. DNA sequences were obtained from each of the 35 class I genes of the BALB/c mouse of the transmembrane domain-encoding fifth exon. Based on nucleotide sequence similarity, the fifth exons could be divided into seven groups that share little similarity with each other. In addition, the majority of the fifth exons are able to encode a transmembrane domain that can be separated into a proline-rich connecting peptide, a hydrophobic transmembrane segment, and a ctyoplasmic portion that includes basic anchoring residues. Since this conservation occurs in spite of extensive variation of nucleotide sequence in these exons, it is likely that selective pressure exists to maintain a functional structure in the majority of class I genes. A cDNA library was constructed from a thymus from a five-week-old BALB/c mouse. From this library, 69 class I cDNA transcripts from 15 different class I genes were isolated and analyzed. Included were three novel

Class I major histocompatibility molecules (MHC) are 45 kilodalton (kD) glycoproteins that associate with a smaller 12 kD polypeptide, [beta]2-microglobulin. In the BALB/c mouse, there are three classical class I molecules, H-2K [superscript d], D [superscript d], and L [superscript d], which are expressed throughout the body and present viral antigens to cytotoxic T lymphocytes (CTLs). In addition to the genes that encode the three classical class I antigens, the BALB/c genome contains 32 genes that structurally resemble the classical class I genes, and therefore possibly encode class I molecules. A few of the non-classical class I genes have been shown to encode molecules, TL, Qa-1, Qa-2, Q10, Qb-1, and Hmt, which are expressed in a generally tissue-specific manner, and probably do not act as restriction elements. However, it is unclear what function these molecules play, or why such a large gene family is maintained if only three viral antigen-presenting restriction elements are required by the murine immune system. DNA sequences were obtained from each of the 35 class I genes of the BALB/c mouse of the transmembrane domain-encoding fifth exon. Based on nucleotide sequence similarity, the fifth exons could be divided into seven groups that share little similarity with each other. In addition, the majority of the fifth exons are able to encode a transmembrane domain that can be separated into a proline-rich connecting peptide, a hydrophobic transmembrane segment, and a ctyoplasmic portion that includes basic anchoring residues. Since this conservation occurs in spite of extensive variation of nucleotide sequence in these exons, it is likely that selective pressure exists to maintain a functional structure in the majority of class I genes. A cDNA library was constructed from a thymus from a five-week-old BALB/c mouse. From this library, 69 class I cDNA transcripts from 15 different class I genes were isolated and analyzed. Included were three novel