Internal organization of the major adult alpha- and beta-globin genes of X. laevis.

We describe the isolation of two recombinant lambda phages, each containing genomic DNA fragments encoding both the major adult alpha- and beta-globin mRNAs of X. laevis. The DNA fragment in the two clones have restriction maps which indicate that they are each derived from a different member of the pair of alleles present in the heterozygote used as the source of DNA for cloning. The characterization of these two clones by restriction mapping, R looping and DNA sequencing shows that the alpha 1- and beta 1-globin genes lie in the orientation separated by 7.7 kb of DNA. There are two introns in the alpha 1-globin gene and two in the beta 1-globin gene, and they interrupt the genes at exactly the same positions as the introns found in all known mammalian alpha- and beta-globin genes. The exon sequences proximal to the introns show a much higher degree of homology with mammalian sequences than the sequences distal to intron/exon junctions, and the introns in the beta 1-globin gene of X. laevis are very similar in length to the corresponding introns in the beta-globin genes of several mammals and the chicken.