SCAPHARCA INAEQUIVALVIS TETRAMERIC HEMOGLOBIN-A AND HEMOGLOBIN-B GENES - EVIDENCE FOR A MINIGENE

Vertebrate and many invertebrate globin genes have a three-exon/two-in tron organization, with introns in highly conserved positions. Accordi ng to the ''intron early'' hypothesis, introns are the vestigial segme nts which flank previously independent coding sequences, thus providin g evidence for the assembly of the ancient proteins by ''exon shufflin g.'' In this paper, we report the analysis of the genes of the bivalve mollusk Scapharca inaequivalvis tetrameric hemoglobin (HbII), which s upport this hypothesis, at least for the hemoglobin genes. We show the existence of ''minigenes'' in the IIA and IIB globin genes, spanning part of the first and second introns, ''in frame'' with the hems-bindi ng domain coded by the second exon. Further support for the exon shuff ling hypothesis can be found in the degree of identity of the ''new'' translated sequences with those flanking the central protein domain of some invertebrate hemoglobins.