Sequence organization and genomic complexity of primate θ1 globin gene, a novel α-globin-like gene

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Abstract
The alpha-like and beta-like globin genes have provided a paradigm for the study of molecular evolution and regulation of multigene families in eukaryotes. The human alpha-globin gene cluster, which is on chromosome 16 (ref. 1), consists of six genes arranged in the order 5'-zeta(embryonic)-psi zeta-psi alpha 2-psi alpha 1-alpha 2(adult)-alpha 1(adult)-3'. DNA sequencing data have demonstrated that zeta (ref. 6) and alpha 2 (or alpha 1, refs 7-9) are the embryonic and adult genes, respectively, while psi zeta (ref. 6), psi alpha 2 (ref. 5) psi alpha 1 (ref. 10) are all inactive pseudogenes. Restriction mapping analysis has shown that the structure of this locus in several anthropoid primates is nearly identical to that of the human. Recently, we have isolated the adult alpha-globin gene region from orang-utan, olive baboon and rhesus macaque by molecular cloning. We report here the complete nucleotide sequence of a gene located immediately downstream from the adult alpha 1-globin gene of the orang-utan, along with its flanking DNA. We designate this gene as theta 1, and show that it contains the essential sequence elements required for an expressive gene. The putative polypeptide is 141 amino acids long, identical to that of the alpha- or zeta-globin, but its predicted amino-acid sequence is nearly as different from the orang-utan alpha-globin (55 differences) as the human zeta-globin is from the human alpha-globin (59 differences), suggesting an ancient history for the theta 1-globin gene. Results of blot hybridization experiments using the cloned orang-utan theta 1 gene sequence as probe demonstrate a similar alpha 2-alpha 1-theta 1 linkage map existing in the human genome. Furthermore, multiple copies of sequences homologous to the theta 1 gene are detected in both human and orang-utan. These results cast a new light on the primate alpha-globin gene family, and have intriguing implications for the existence of previously unreported, functional globin-like gene(s) in the primate genomes.