The yeast Saccharomyces cerevisiae and Schizosaccharomyces pombe transformed by plasmids containing retrotransposon from yeast or Drosophila under the control of a strong promoter show the remarkable reverse transcriptase activity. The activity results in the impaired yeast growth and decreased mitotic stability of the plasmids. The phenotypic expression of the reverse transcriptase activity is observed within 30 days.