The primary structure of the larval beta 1-globin gene of Xenopus laevis and its flanking regions.

We present the complete nucleotide sequence of the larval beta I-globin gene of Xenopus laevis including 240 nucleotides of the 5' flanking region and 594 nucleotides beyond the polyadenylation site. The site of transcription initiation was mapped by S1 nuclease, and the site of polyadenylation was determined by comparison with corresponding cDNA clones. The larval Xenopus beta I-gene shows the same internal structure as the beta-globin genes of higher vertebrates, viz. 3 exons interrupted by 2 intervening sequences. The first intervening sequence, which is of exceptional length, spans over 564 nucleotides and interrupts the coding sequence at amino acid 30, whereas the second one comprises 968 nucleotides and is located between the amino acids 104 and 105. The second intervening sequence contains a long inverted repeat of almost perfect homology. The 5' flanking region contains a TATA- and a CAAT-box at positions -33 and -58, respectively. An additional TATA-box is located at -197 and two more CAAT-boxes occur at positions -105 and -237.