Unusual structure of the chicken embryonic alpha-globin gene, pi'

We report the DNA sequence of the globin locus encoding the chicken embryonic alpha-globin, pi'. The structure differs significantly from that of the two chicken adult alpha-globin genes, alpha A and alpha D, as well as from that of previously studied adult alpha-globin genes in that the introns of the pi' gene are substantially larger than those in adult alpha-globin loci. In contrast, the pi' introns are structurally similar to the only other expressed embryonic alpha-globin gene reported to date, the human zeta gene. While completing the sequence of the pi' gene, we determined that only one chromosomal locus within the chicken genome hybridizes to a pi' central exon probe. These data lead to the conclusion that if the equimolar chicken embryonic alpha-globin polypeptides, called pi and pi', are indeed independently transcribed, then that transcription occurs from alleles of the same gene; however, we favor the possibility that the pi gene does not actually exist. This conclusion is drawn from the observation that the two chromosomal alleles of embryonic alpha-globins (represented by recombinant bacteriophage lambda CaG5 and lambda CaG7) both encode pi'.