Nucleotide Sequence and Expression of Rabbit Globin Genes ζ1, ζ2, and ζ3: Pseudogenes Generated by Block Duplications are Transcriptionally Competent

The addition of two embryonic globin genes, zeta 0 and zeta 4, to the rabbit alpha-like globin gene cluster expands it to include eight genes arranged 5'-zeta 0-zeta 1-alpha 1-theta 1-zeta 2-zeta 3-theta 2-zeta 4-3'. The identification of these new genes supports the model that this gene cluster evolved by a series of block duplications of gene sets. The nucleotide sequence of three embryonic zeta-globin genes, zeta 1, zeta 2, and zeta 3, shows that all three are pseudogenes. Gene zeta 1 contains two frame-shift deletions, gene zeta 2 has lost exon 1 as well as the 5' promoter sequences, and gene zeta 3 has lost and replaced codons for amino acids that are critical for the function of alpha- and zeta-globin polypeptides. However, genes zeta 1 and zeta 3 are still transcriptionally competent, as shown by the accurate initiation and processing of transcripts from cloned genes introduced into HeLa cells. A quantitative comparison of the zeta-globin gene sequences indicates that the ancestor to the rabbit zeta 1 and zeta 3 genes was inactivated about 44 million years ago, and the block duplication that formed the two genes occurred about 28 million years ago. About 600 base pairs of the 5'-flanking sequence of the rabbit zeta 3-globin gene is very similar to the 5' flanks of three other mammalian zeta-globin genes.