Nonmethylated Transposable Elements and Methylated Genes in a Chordate Genome

Science  19 Feb 1999:
Vol. 283, Issue 5405, pp. 1164-1167
DOI: 10.1126/science.283.5405.1164

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The genome of the invertebrate chordate Ciona intestinalis was found to be a stable mosaic of methylated and nonmethylated domains. Multiple copies of an apparently active long terminal repeat retrotransposon and a long interspersed element are nonmethylated and a large fraction of abundant short interspersed elements are also methylation free. Genes, by contrast, are predominantly methylated. These data are incompatible with the genome defense model, which proposes that DNA methylation in animals is primarily targeted to endogenous transposable elements. Cytosine methylation in this urochordate may be preferentially directed to genes.

  • * These authors contributed equally to this work.

  • To whom correspondence should be addressed. E-mail: A.Bird{at}

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