期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1990
卷号：87
期号：24
页码：9798-9802
DOI：10.1073/pnas.87.24.9798
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：As part of our studies of the class II genes of miniature swine, we have isolated and characterized cDNA clones corresponding to DRB genes from two major histocompatibility complex homozygous strains. Comparison of the sequences of these clones to those of human DRB genes revealed a striking amino acid homology between the hypervariable residues of SLA-DRBc and the human DRB1-0101 allele. The percentage of differences in these residues between the pig DRBc allele and the human DRB1-0101 allele was significantly lower (29%) than that between the DRB1-0101 allele and all other human alleles (average, 66.2%). This similarity was not seen in a comparison of the number of silent substitutions, by which the swine DRBc and the human DRB-0101 differed. Since phenotypic selection operates at the level of protein products rather than nucleotide sequences, these data suggest the existence of selective mechanisms that have resulted in similar hypervariable regions in certain alleles even in these widely disparate species. Consistent with this hypothesis, an examination of available murine and bovine class II sequences revealed a homology in hypervariable residues between the human DRB1-1401 allele and the mouse E beta s allele as well as a cow DRB allele. Consideration of these data along with intraspecies allelic sequence comparisons suggests that at least some of the interspecies similarities have emerged as the result of convergent evolution, possibly as the result of a need to react to common pathogens.
