The isolation and characterization of linked delta- and beta-globin genes from a cloned library of human DNA

A cloned library of large, random embryonic human DNA fragments was constructed and screened for beta-globin sequences using the cloned human beta-globin cDNA plasmid pJW102 (Wilson et al., 1978) as a hybridization probe. Two independent clones were obtained and then characterized by restriction endonuclease cleavage analysis, hybridization experiments and partial DNA sequencing. Each of the clones carries both the adult delta- and beta-globin genes. The two genes are separated by approximately 5.4 kilobases (kb) of DNA and their orientation with respect to the direction of transcription is 5'-delta--beta-3'. Both the delta- and beta-globin genes contain a large noncoding intervening sequence (950 and 900 bp, respectively) located between the codons for amino acids 104 (arginine) and 105 (leucine). Although the location of the large intervening sequence within the coding regions of the two genes is identical, the two noncoding sequences bear little sequence homology. A second, smaller intervening sequence similar to that found in other mammalian beta-globin genes was detected near the 5' end of the human beta-globin gene. The two independently isolated beta-globin clones differ from each other by the presence of a Pst I restriction enzyme cleavage site within the large intervening sequence of the delta-globin gene of one of the clones. This suggests that the human DNA carried in the two clones was derived from two homologous chromosomes which were heterozygous for the Pst I restriction enzyme recognition sequence.