Isolation and characterization of three class II MHC genomic clones from the chicken.

A genomic library was constructed from sperm DNA from an individual of the inbred chicken line G-B2, MHC haplotype B6. The library was screened with a chicken class II probe (beta 2 exon specific) and three MHC class II beta chain genomic clones were isolated. The restriction maps of the three clones showed that each of the three clones was unique. The position of the beta chain sequence was located in each of the three genomic clones by Southern blot hybridization. Subclones containing the beta chain gene were produced from each of the genomic clones and the orientation of the leader peptide, beta 1, beta 2, transmembrane, and cytoplasmic exons was determined by Southern blot hybridization and nucleotide sequencing. The complete nucleotide sequence of two of the three subclones was determined. Comparison of the nucleotide and predicted amino acid sequences of the two subclones with other class II beta chain sequences showed that the B6 chicken beta chain genes are evolutionarily related to the class II beta chain genes from chickens of other MHC haplotypes, and to class II beta chain genes from other species. Analysis of Southern blots of B6 chicken DNA, as well as the isolation of the three beta chain genes, suggests that chickens of the B6 haplotype possess at least three MHC class II beta chain genes.