CHICKEN MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II B-GENES - ANALYSIS OF INTERALLELIC AND INTERLOCUS SEQUENCE VARIANCE

Five different chicken B-LB genes were cloned and sequenced. The compa rison of these sequences shows that they can be classified as members of two different families, the B-LBII family (containing the B-LBI and B-LBII genes) and the B-LBIII family (containing the B-LBIII, B-LBIV, and B-LBV genes).The extent of polymorphism within each of these fami lies was assessed by in vitro amplification of DNA fragments encompass ing exon 2 in several haplotypes.The nucleotide sequences were determi ned, and pairwise relationships were evaluated. In the course of this work, a sixth gene termed B-LBVI was identified, defining a third fami ly (B-LBVI family). Polymorphism of the B-LBIII or B-LBVI families is far less extensive than that of the B-LBII family. In this latter, the distribution of conserved and polymorphic residues is similar to what has been described in mammals. These families seem to have been gener ated by gene duplication events giving rise to several isotypes, as ob served in mammals. However, phylogenetic analyses indicate that these families are not homologous to their mammalian counterparts. Evaluatio n of the level of transcription of these different genes showed that g enes from the B-LBII family are predominantly transcribed over those o f the other families.