THE EXON INTRON ORGANIZATION OF THE GLOBIN GENE OF SCAPHARCA-INAEQUIVALVIS HOMODIMERIC HEMOGLOBIN - UNUSUAL INTRON HOMOLOGY WITH OTHER BIVALVE MOLLUSE GLOBIN GENES/

In this study, we have investigated the positions of introns in the gl obin gene of Scapharca inaequivalvis homodimeric hemoglobin. We found the three exon/two intron organization typical of vertebrate globin ge nes, with the two introns in highly conserved positions, as it occurs in the A and B globin genes of the tetrameric hemoglobin from the same organism, confirming the absence of the so-called 'central intron' fo und in the globin genes of plants and of some invertebrates. We identi fied two homodimeric globin genes (3207 and 2723 bp) that differ only with respect to the size of the first intron. Sequence analysis of the two first introns (1668 and 1364 bp) has revealed that they are highl y homologous, except for a 569- and 296-bp insertion in each intron I. Interestingly, the two first introns contain regions with an unusuall y high identity (similar to 80%) with regions of the first intron of t he congeneric clam Anadara trapezia and the related clam Barbatia reve ana globin genes, suggesting that these uncoding regions may have play ed a regulatory role that has subsequently been lost during the course of the evolution. (C) 1998 Elsevier Science B.V. All rights reserved.