A previously undetected pseudogene in the human alpha globin gene cluster.

The sequence of the DNA between two pseudogenes in the human alpha-like globin gene cluster has been determined. Comparison of this sequence with sequences from other alpha-like globin gene clusters revealed another pseudogene, psi alpha 2, between the previously recognized pseudogenes zeta 1 and psi alpha 1. Therefore, the human alpha-like globin gene family is organized 5'-zeta 2-zeta 1-psi alpha 2-psi alpha 1-alpha 2-alpha 1-3'. The new pseudogene psi alpha 2 is very close to zeta 1, beginning only 65 base pairs 3' to the polyadenylation site of zeta 1. The first exon and the first intron of psi alpha 2 are interrupted by large inserts which are flanked by short (6 to 8 base pairs) direct repeats. The pseudogene psi alpha 2 lacks a promoter for transcription by RNA polymerase II, the first exon is highly divergent, one splice site is mutated, and five different frameshift mutations have occurred in the coding regions. Thus psi alpha 2 cannot encode a globin polypeptide. This pseudogene was not recognized in previous hybridization analyses of the human alpha-like globin gene cluster, and our discovery of it by sequence analysis suggests that divergent copies of a large number of genes may comprise a substantial fraction of the slowly renaturing DNA of mammalian genomes.