BOTH DQB GENES ARE EXPRESSED IN BOLA HAPLOTYPES CARRYING A DUPLICATEDDQ REGION

The objective of this study was to determine whether more than one DQB gene is expressed in three BoLA haplotypes that have a duplicated DQ region. Leukocyte mRNA from three animals genotyped at the BoLA-A, DQB , and DRB3 loci was used as template for reverse transcription-polymer ase chain reaction (RT-PCR), cloning, and DNA sequencing. Five DQB all eles were identified. All cDNA clones were 564 base pairs (bp) in leng th, including 507 bp of nonprimer-derived sequence that contained the coding sequence for the full length of exon 2 and 74 amino acids of ex on 3. Three alleles were assigned to the DQB1 locus and two were assig ned to DQB2 on the basis of sequence comparisons with previously repor ted alleles. The expression of DQB1 and DQB2 in individual animals was examined by RT-PCR followed by double digestion of the 564 bp PCR pro ducts with Eco O109 I and Dra III in order to discriminate the DQB all eles. Evidence that DQB1 and DQB2 are both transcribed was obtained fo r three different BoLA haplotypes with DQB duplications, DQB10, DQB11C , and DQB12. These results suggest that the duplication or deletion ev ent that gave rise to the DQB1 and DQB2 genes is a relatively recent e vent in the evolution of the cattle MHC.