NUCLEOTIDE-SEQUENCE AND THE MOLECULAR EVOLUTION OF A NEW A2 GENE IN THE DQ SUBREGION OF THE BOVINE MAJOR HISTOCOMPATIBILITY COMPLEX

cDNA clones encoding the bovine major histocompatibility complex (MHC) class II DQ alpha chain were isolated. One clone, MQ9, encoded a prim ary translated product of 255 amino acids, with a signal peptide of 23 amino acids and a mature polypeptide of 232 amino acids. A new A2 gen e in the DQ subregion of the bovine genome was identified from a compa rison of amino acid sequences encoded by class II A genes among severa l species and the construction of a phylogenetic tree. It was revealed that MQ9 is most closely related to the ovine DQA2 genes among sequen ces from various mammalian species. By contrast, the BoLA-DQA genes pr eviously isolated are more closely related to ovine DQA1 than to the B oLA-DQA2 gene, and they represent BoLA-DQA1 genes. Thus, the presence of two BoLA A genes, which may be expressed and functional in the bovi ne, as well as in sheep was confirmed. A large number of amino acids u nique to products of DQA2 genes of bovine and ovine origin were identi fied when the predicted amino acid sequences for both species were com pared, and most of the DQA2-specific residues were located in the al d omain and were conserved with respect to products of DQA1 genes of rum inants. Thus, several characteristics of the bovine DQA genes were fou nd to differ from those of human and rodent genes, despite similaritie s in gene structure and in nucleotide sequence. (C) 1995 Academic Pres s, Inc.