Polymorphisms of the upstream regulatory region of the major histocompatibility complex DRB genes in domestic horses.

Sequence information was obtained on the variation of the ELA-DRB upstream regulatory region (URR) after polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) cloning and sequencing of approximately 220 bp upstream of the first exon of horse DRB genes. The sequence of the proximal URR of equine DRB is composed of highly conserved sequence motifs, showing the presence of the W, X, Y, CAAT and TATA conserved boxes of major histocompatibility complex (MHC) class II promoters. Five different polymorphic horse DRB promoter sequences were detected in five horse breeds. The results demonstrate the existence of polymorphism in the nucleotide sequences of the ELA-DRB URR, located in the functionally important conserved consensus sequences, the X2 box, the Y box and the TATA box, while conservation were observed in X1 and CAAT boxes. The nucleotide diversity among horse URRs was intermediate between that seen within human and mouse DRB promoters, suggesting the existence of another important source of variability in ELA-DRB genes. In addition, phylogenetic comparisons, identity analysis and sequence organization suggested that the reported sequences would correspond to an expressed ELA-DRB locus. However, further information about the functional significance of these promoter polymorphisms will probably be acquired through expression studies on the different sequences.