Three a-type globin genes have been identified in the a-globin linkage group of chickens. No other a-type genes have been directly shown to be within 10 kilobase pairs of any of these three closely linked genes. These three genes have been conclusively identified by DNA sequence analysis. The gene at the 5' end of the linkage group is an embryonic a-type globin gene, ar or ir, and the central gene corresponds to the minor adult aglobin, aD. The 3'-terminal gene sequence corresponds to the sequence of cDNA clones previously described as "71", a presumed anemic shock-induced a-globin gene

We report the DNA sequence of the globin locus encoding the chicken embryonic a-globin, i. The structure differs significantly from that of the two chicken adult a-globin genes, aA and aD, as well as from that of previously studied adult a-globin genes in that the introns of the m-" gene are substantially larger than those in adult a-globin loci. In contrast, the i' introns are structurally similar to the only other expressed embryonic a-globin gene reported to date, the human 'gene. While completing the sequence of the l' gene, we determined that only one chromosomal locus within the chicken genome hybridizes to a i' central exon probe. These data lead to the conclusion that if the equimolar chicken embryonic a-globin polypeptides, called wfand i', are indeed independently transcribed, then that transcription occurs from alleles of the same gene; however, we favor the possibility that the w gene does not actually exist. This conclusion is drawn from the observation that the two chromosomal alleles of embryonic a-globins (represented by recombinant bacteriophage ACaG5 and ACaG7) both encode i'.The a-and f3-globin genes of the chicken make up a small multigene family that is subject to temporal regulation of gene expression during development (switching). This regulation can be defined as occurring both within a single cell type (e.g., transient pH expression in the definitive erythroid cell) and in differentially related cell types [e.g., p versus /3 expression during the switch from embryonic globin synthesis in primitive erythroid cells to adult globin synthesis in definitive erythroid cells (1)]. To study the expression of those genes that are regulated during avian embryogenesis, we have isolated and characterized both a-and /3-globin linkage groups on recombinant bacteriophage (2-5).In this paper, we report the complete DNA sequence for the member of the globin gene family of the chicken that had not heretofore conclusively been identified in chromosomal DNA, that encoding the embryonic chicken a-globin. The gene sequence here reported encodes 7r', one of two major a-globins expressed exclusively in the primitive erythroid line. These two globins are reported to differ one from another by a single amino acid at position 124 of the polypeptide chain, being either alanine (vr) or glutamate (ir') (6).We (2) has been described (4,5). The position of the ir or r' gene within these recombinants was determined by positive blot hybridization with a radioactive cDNA probe prepared from globin mRNA isolated from embryos 4.5 days after fertilization, and lack of hybridization to the same restriction fragments with an adult globin-specific cDNA probe (ref. 4; data not shown). The chromosomal a-globin domain as defined by these hybridizations is shown by Fig. 1A, and, in particular, the locus reported herein is shown in Fig. 1B. Subelones prepared from this segment of the chromosome and containing the embryonic aglobin locus are shown in Fig. 1C, and sequence analysis strategy for the locus is shown in Fig. 1D....