Structure and expression of a divergent canine class I gene.
We have isolated and characterized a canine class I MHC (dog leukocyte Ag, DLA) gene, DLA-79. The deduced protein sequence shares only 65% identity with a previously published canine class I cDNA, designated DLA-A, and exhibits 64% amino acid identity with the HLA-A, -B, -C consensus. The peptide-binding region of DLA-79 is unusual. Three of four highly conserved tyrosine residues (Tyr7, 59, 159, and 171), proposed to interact with the N terminus of peptide-Ag, are substituted. Additionally, the long alpha-helix lining the peptide-binding region in the alpha 1 domain contains one more amino acid residue than that observed in typical class I. Together, these features suggest that DLA-79 binds a distinct subset of peptides or other ligands. This gene has been expressed in a class I null human lymphoblastoid cell line, and the encoded heavy chain associated with beta 2-microglobulin and was transported to the cell surface. Ribonuclease protection analysis detected low levels of gene-specific mRNA in a broad variety of dog tissues. The highest levels were found in skeletal muscle, a tissue expressing relatively low levels of classical class I Ag. These data suggest that DLA-79 is functional and plays a specialized role in the immune response. Nucleotide sequence analysis of second exon sequences (encoding the alpha 1 domain) identified only two alleles in five dogs of different breeds; a third variant was found in a coyote. The divergent structure, relatively low mRNA expression, and limited polymorphism of this gene suggest that DLA-79 is not a classical or class Ia gene, but rather, an analogue of the MHC class Ib genes of humans and rodents.
Burnett
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Transplantation Biology Program, Fred Hutchinson Cancer Research Center, Seattle, WA 98104, USA.
Geraghty
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D004285:Dogs; D005805:Genes, MHC Class I; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic / Q000276:immunology*; D017386:Sequence Homology, Amino Acid
D015395:Histocompatibility Antigens Class I