Molecular analysis and polymorphism of the DLA-DQB genes

Partial-length cDNA clones and full-length genomic clones corresponding to a complete canine DQB class II gene were isolated. Southern analyses suggested the presence of two DQB genes - one of which appeared to be a pseudogene lacking exon 2 called DQB2. The other DQB gene, called DQB1, was isolated from a genomic phage clone and contained six exons. The DQB1 clone was restriction mapped, and exon 2 was sequenced from 70 dogs. Twenty alleles were found. Most of the amino acid substitutions occurred at putative positions in the peptide binding site. Inheritance of these sequences showed Mendelian segregation with one or two alleles per dog. Cluster analysis of the nucleotide and predicted amino acid sequences subdivided the canine DQB1 alleles into four major allelic groups. The number of nonsynonymous changes was higher than the number of synonymous changes in the putative antigen recognition sites suggestive of positive selection.