Ty1 insertions in intergenic regions of the genome of Saccharomyces cerevisiae transcribed by RNA polymerase III have no detectable selective effect

The retrotransposon Tyl of Saccharomyces cerevisiae inserts preferentially into intergenic regions in the vicinity of RNA polymerase III-transcribed genes. It has been suggested that this preference has evolved to minimize the deleterious effects of element transposition on the host genome, and thus to favor their evolutionary survival. This presupposes that such insertions have no selective effect. However, there has been no direct test of this hypothesis. Here we construct a series of strains containing single Tyl insertions in the vicinity of tRNA genes, or in the rDNA cluster on chromosome XII, which are otherwise isogenic to strain 337, containing zero Tyl elements. Competition experiments between 337 and the strains containing single Tyl insertions revealed that in all cases, the Tyl insertions have no selective effect in rich medium. These results are thus consistent with the hypothesis that the insertion site preference of Tyl elements has evolved to minimize the deleterious effects of transposition on the host genome. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.