Hemoglobin switching in sheep. Isolation of the fetal gamma-globin gene and demonstration that the fetal gamma- and adult beta A-globin genes lie within eight kilobase segments of homologous DNA.

A recombinant DNA library of sheep genomic DNA fragments inserted into the bacteriophage vector, Charon 4A, was screened by plaque hybridization with a probe for sheep gamma-globin gene sequences. Three clones containing overlapping segments of DNA, the total length of which was 25 kb, were identified; each included all or a part of the same globin gene. Nucleotide sequencing of substantial portions of the globin gene in one clone, lambda S gamma G31, and of the gene in a previously isolated recombinant, lambda S beta AG21, established that the genes in these recombinants encoded for the gamma- and beta A-globin genes of sheep, respectively. Features characteristic of globin genes in other species that were identified in both genes included a sequence, ATAAAA, 30 nucleotides from the presumed site of initiation of transcription, a region of "capping homology," two introns at positions corresponding to amino acids 29-30 and 103-104 and the polyadenylation sequence, AATAAA, in the 3' untranslated region. Electron microscopic analysis of heteroduplexes formed between lambda S gamma G31 and lambda S beta AG21 revealed that the gamma and beta A genes of sheep lie within segments of homologous DNA at least 8 kb in length within which were identified small regions of nonhomology both 5' and 3' to the genes.