Molecular cloning and characterization of horse DQB cDNA

A full-length cDNA clone encoding horse Mhc class II DQB antigen has been isolated and sequenced. A lymphocyte-derived cDNA library was constructed from an Eqca class I A2 homozygous stallion and cloned into pcDNA I vector. The probe for screening was obtained by amplifying the second exon of the DQB gene from a 10 super(-4) dilution of the cDNA library itself. The PCR conditions and primer sequences for the second exon of the mammalian DQB loci have been described earlier. The Eqca-DQB cDNA clone was found to be 1239 basepairs long and the most probable protein it encodes consists of 237 amino acids from the first residue of the beta 1 domain. The signal peptide is 28 amino acids long and appears to be shorter by four amino acids when compared with humans. Probably several point mutations occurred during the divergence of humans and the horse, and transferred the start codon by four amino acids. The predicted equine DQB mature peptide has the remarkable feature of eight additional amino acids in the cytoplasmic domain when compared with DQB sequences from other species, with the exception of rodents.