Tandemly duplicated α globin genes of gibbon

The α globin gene locus of the common gibbon (Hylobates lar) was isolated, and it contains two closely linked α globin genes that share the same arrangement as that found for the homologous genes of other catarrhine primates. The nucleotide sequences of the gibbon α globin genes were determined and compared with the α globin gene sequences from other primate species (human, chimpanzee, orangutan, baboon, and rhesus); the prosimian primate, galago, αA and αB globin genes provided the outgroup for this analysis. The degree of divergence for both synonymous and nonsynonymous substitutions among the α globin genes are generally smaller for intraspecies than interspecies comparisons, which is indicative of concerted evolution between the paired α globin genes of each catarrhine species. The pattern of differences is suggestive of gene conversions. This possibility is supported by both site-by-site and branch-swapping parsimony analyses. The site-by-site parsimony analysis was also used to determine the 3' boundary of each catarrhine species-specific conversion. These α globin gene conversion events encompass most of the transcriptional region, including the promoter, exons, introns, and about one-half of the 3'-untranslated region. However, the paired gibbon α globin genes show the highest degree of divergence, differing by five nucleotides in their coding regions, three of which encode amino acid replacement substitutions. It appears that the last convergence event between the paired gibbon α globin genes is relatively ancient, having occurred approximately 11 million years ago. The remaining 3'-untranslated region and flanking DNAs show no evidence of involvement in any recent conversion event as the parsimony analysis of these sequences group all the α1 globin genes of the different catarrhine species into one clade and all the α2 globin gene of these species into a separate clade. The sequence comparison among the α globin genes of different primate species also provides interesting implications regarding the evolution and functional domains of the 3'-untranslated regions.