A VARIABLE INTRON DISTRIBUTION IN GLOBIN GENES OF CHIRONOMUS - EVIDENCE FOR RECENT INTRON GAIN

The intron positions found in globin genes of plants, protozoa and inv ertebrates have been interpreted as evidence for a three-intron-four-e xon structure of the ancestral globin gene. In particular, the so-call ed 'central' introns, which are not found in vertebrate globin genes b ut are present in a variety of invertebrate and plant species, have be en used as an argument for an ancestral gene structure featuring three introns. We have analyzed the presence or absence of central introns in the Gb genes 2 beta, 9 and 7A of various European and Australasian species of the insect Chironomus. We find unrelated central introns at different positions in some of the species investigated, while other species completely lack introns in these genes. This variable distribu tion of introns is parsimoniously explained by independent intron addi tions. Such a gain of introns may occur convergently at identical posi tions in unrelated taxa. Insertion by gene conversion may be a viable mechanism to explain intron gain. (C) 1997 Elsevier Science B.V.