Ty1 extrachromosomal circular copies in Saccharomyces cerevisiae.

The eukaryotic transposable element Ty1 is present in about 20-30 integrated copies per yeast aploid genome, variably localized in different strains. Here, we report the presence in yeast of circular extrachromosomal molecules homologous to Ty1, 6 kilobases in size (the same as integrated copies) present in about 1 circular copy/250-300 cells. This finding shows another analogy between eukaryotic-transposable elements and the pro-viral integrative form of retroviruses.