Junctions between genes in the haptoglobin gene cluster of primates.

To investigate the nature of the recombination that generated the haptoglobin three-gene cluster in Old World primates, we sequenced the region between the second gene (HPR) and the third gene (HPP) in chimpanzees (15 kb), as well as the region 3' to the cluster in humans (14 kb). Comparison to the previously sequenced human haptoglobin (HP) and HPR genes showed that the junction point between HP and HPR in humans (junction 1) was not identical to the junction point between the HPR and HPP genes of the chimpanzee (junction 2). An Alu sequence was found at each junction, but both Alu sequences lacked short direct repeats of the flanking genomic DNA. The lack of direct repeats implies that both junction Alu sequences are the products of recombination between different Alu elements. In addition, other insertion and deletion events are clustered in the regions near the junction Alu sequences. The observation that Alu sequences define the junctions between genes in the haptoglobin gene cluster emphasizes the importance of Alu sequences in the evolution of multigene families.