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The Journal of Heredity 1999:90(3)
© 1999 The American Genetic Association 90:374-379

Genes and proteins of the transcriptional apparatus in mitochondria

TM Ikeda, and MW Gray*

Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada *Corresponding author e-mail: m.w.gray@dal.ca

In this article we review recent advances in our understanding of the biochemistry and evolution of the mitochondrial transcriptional apparatus, with emphasis on flowering plants (angiosperms). In the majority of eukaryotes studied to date, including plants, the mitochondrial RNA (mtRNA) polymerase is a single-polypeptide, bacteriophage T3/T7-like enzyme, encoded in the nucleus. While the evolutionary origin of the T3/T7 RNA polymerase itself remains an enigma, the emergence of a phagelike mtRNA polymerase seems to have closely paralleled the appearance of mitochondria within the eukaryotic cell. In angiosperms, several groups have discovered a second phagelike RNA polymerase gene, evidently arising via duplication of a preexisting gene encoding the mtRNA polymerase. This second gene specifies a phagelike activity that functions in the chloroplast, in addition to the eubacteria-like RNA polymerase encoded by the chloroplast genome. The chloroplast situation appears to recapitulate an early stage in the evolution of the mitochondrial transcriptional machinery: that is, appearance of a phagelike enzyme that eventually displaced a multisubunit, eubacteria-like RNA polymerase originally encoded in the protomitochondrial genome. In angiosperms, candidate transcription factors (promoter-specific DNA-binding proteins) have been characterized in wheat (63 kDa) and pea (34 and 44 kDa). This difference between monocotyledonous and dicotyledonous plants may reflect known differences in the promoter sequences recognized by the mtRNA polymerase in the two angiosperm groups.


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