EASEL, A GYPSY LTR-RETROTRANSPOSON IN THE SALMONIDAE

Despite the close similarities between retroviruses and the gypsy/Ty3 group of LTR-retrotransposons their host ranges are largely distinct: the retroviruses are found only in vertebrates, whereas the gypsy LTR- retrotransposons are almost exclusively restricted to invertebrates, p lants and fungi. Here we report the amplification by PCR, and characte risation, of one of the first LTR-retrotransposons to be discovered in vertebrates - in several members of the piscine family Salmonidae. Ph ylogenetic analysis of this retroelement, termed easel, indicates that it is probably a phylogeneticaly basal member of the gypsy group of L TR-retrotransposons and occurs in some of the same species from which retroviruses have previously been isolated. Thus some members of the S almonidae are the first organisms known to harbour both retroviral bra nch elements and the gypsy LTR-retrotransposon branch elements. This c reates an overlap in the host ranges of the two retroelement families.