After analyzing the base composition asymmetry of coding regions in vertebrate mitochondria, we identified 2 fishes, Albula glossodonta and Bathygadus antrodes, with inverted compositional patterns. Both species appear to have an unusual control region (CR), and in B. antrodes, it has switched from the light strand to the heavy strand. To our knowledge, this is the first report in vertebrates of inverted mitochondrial replication, caused by an inversion of the CR. These findings support the strand-asymmetric model of mtDNA replication and suggest that vertebrate mtDNA can tolerate globally reversed mutational pressures. In addition, we propose that nucleotide bias is not strand specific but that it depends on the location of the CR.
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