SCAPHARCA INAEQUIVALVIS TETRAMERIC HEMOGLOBIN-A AND HEMOGLOBIN-B CHAINS - CDNA SEQUENCING AND GENOMIC ORGANIZATION

A and B globin cDNAs from the tetrameric hemoglobin of the bivalve mol lusc Scapharca inaequivalvis were isolated by RT-PCR and sequenced. Wh en compared with the biochemical data, the deduced protein sequences r evealed only one amino acid substitution in the B chain. In order to i nvestigate the genomic structure of these invertebrate globin genes, t heir intronic regions were amplified by PCR. The two genes showed the typical two-intron/three-exon organization found in vertebrates and se emed to reflect the ancestral gene structure, in accordance with the n ew globin gene evolution theory proposed by Dixon and Pohajadak (Trend s Biochem. Sci. 17:486-488, 1992). The alternative hypothesis suggeste d by Go (Nature 291:90-92, 1981), that the central intron was lost dur ing evolution, is also considered. In contrast to the related clam Ana dara trapezia, S. inaequivalvis A and B globin genes were found to be present in multiple copies differing in intron size. In this study we report the complete sequences of the A (1,471 bp) and B (2,221 bp) glo bin genes, giving a detailed analysis of their intron features.