The Marsupial Mitochondrial Genome and the Evolution of Placental Mammals 

Axel Janke,1 Gertraud Feldmaier-Fuchs,1 W. Kelley Thomas,2 Arndt von Haeseler1 and Svante Piiibo1 

Zoologisches Znstitut, Uniuersitat Munchen, PF 202136, 0-80021 Munchen, Germany, and

Diuision of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri, Kansas City, Missouri 641 10-249


The entire nucleotide sequence of the mitochondrial genome of the American opossum, Didelphis virginiana, was determined. Two major features distinguish this genome from those of other mammals. First, five tRNA genes around the origin of light strand replication are rearranged. Second, the anticodon of tRNAsp is posttranscriptionally changed by an RNA editing process such that its coding capacity is altered. When the complete protein-coding region of the mitochondrial genome is used as an outgroup for placental mammals it can be shown that rodents represent an earlier branch among placental mammals than primates and artiodactyls and that artiodactyls share a common ancestor with carnivores. The overall rates of evolution of most of the mitochondrial genome of placentals are clocklike. Furthermore, the data indicate that the lineages leading to the mouse and rat may have diverged from each other as much as - 35 million years ago