Studying the genetic polymorphism of the major histocompatibility complex class II genes in cattle, we identified a sequence (KUH1) which resembles those encoding class II β chains. The gene was shown to be transcribed in peripheral blood leukocytes. Sequence comparisons, Southern blot, and phylogenetic analyses indicate that (1) KUH1 represents a distinct DQB locus, which we propose to designate BoLA-DQB5, (2) DQB5 constitutes an ancient DQB locus which diverged from a common ancestor gene prior to the duplication resulting in DQB1 and DQB2, (3) DQB5 is associated with haplotypes which contain DQA5 and a duplicated DQ region.
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