The nucleotide sequence of the embryonic chicken beta-type globin genes

Abstract

The complete nucleotide sequence is reported for both of the embryonic chicken beta-type globin genes, rho and epsilon. These two genes lie at the 5' end and 3' end, respectively, of the four closely linked chicken beta-type globin genes relative to the direction of transcription. Both genes have structures that are typical of functional beta-type globin genes in that they contain two intervening sequences with the 5'-most intron being relatively small (108 base pairs in both) and the 3' intron being large (541 base pairs in rho and 973 base pairs in epsilon). Both embryonic genes contain consensus flanking sequences which are similar to those previously found in the adult chicken beta-globin gene and in a variety of other genes transcribed by RNA polymerase II. The rho- and epsilon-globin gene sequences are very similar from approximately nucleotide -130 (with the mRNA initiation site as +1) to the end of exon II. Noncoding sequences outside this region (e.g. intron II and DNA 5' to -130) are highly divergent. This may indicate that the DNA sequence elements which specifically activate embryonic beta-type globin gene expression in primitive red cells are contained within the -130 to +468 region. Comparison of the overall sequences of rho and epsilon to that of beta strongly supports the hypothesis that the embryonic avian beta-type globin genes diverged from the adult beta-gene by a process separate from that which was responsible for the generation of nonadult mammalian beta-type globin genes.