Analysis of polymorphisms in the major expressed class I locus (B-FIV) of the chicken.
We analyzed the polymorphic nature of eleven alleles expressed by the major class I locus (B-FIV) in chickens. Similar to mammalian class I loci, the nucleotide substitutions with high variability occur in exons 2 and 3 encoding the alpha1 and alpha2 domains. However, the nonsynonymous to synonymous ratio of nucleotide substitutions in exon 3 encoding the alpha helix and beta sheets is reversed compared with HLA. The region of exon 3 encoding the alpha2 helix demonstrates a much lower nonsynonymous to synonymous ratio, suggesting evolutionary selection of a more conserved alpha2 helix in B-FIV compared with HLA. Amino acid residues with high Wu-Kabat variability are typically located in positions predicted to impact antigen presentation. B-FIV amino acid residues predicted to interact with the CDR1alpha region of the T-cell receptor (Tcr) demonstrate less variability than in mouse and human class I alleles. The combination of a reduced nonsynonymous to synonymous ratio in exon 3 encoding the alpha2 helix and the limited variability in CDR1alpha contact residues is discussed with regard to concerted evolution between a minimal major histocompatibility complex and compaction of Tcr variable gene segments in the chicken.
Hunt
H D
HD
United States Department of Agriculture, Agriculture Research Service, Avian Disease and Oncology Laboratory, East Lansing, MI 48823, USA.
Fulton
J E
JE
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002645:Chickens / Q000235:genetics* / Q000276:immunology*; D017124:Conserved Sequence; D018076:DNA, Complementary; D005805:Genes, MHC Class I; D006801:Humans; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D018076:DNA, Complementary