Although mitochondria and chloroplasts are considered to be descendants of eubacteria-like endo- symbionts, the mitochondrial RNA polymerase of yeast is a nucleus-encoded, single-subunit enzyme homologous to bacteriophage T3 and T7 RNA polymerases, rather than a multi-component, eubacterial-type alpha 2 beta beta' enzyme, as encoded in chloroplast DNA. To broaden our knowledge of the mitochondrial transcriptional apparatus, we have used a polymerase chain reaction (PCR) approach designed to amplify an internal portion of phage T3/T7-like RNA polymerase genes. Using this strategy, we have recovered sequences homologous to yeast mitochondrial and phage T3/T7 RNA polymerases from a phylogenetically broad range of multicellular and unicellular eukaryotes. These organisms display diverse patterns of mitochondrial genome organization and expression, and include species that separated from the main eukaryotic line early in the evolution of this lineage. In certain cases, we can deduce that PCR-amplified sequences, some of which contain small introns, are localized in nuclear DNA. We infer that the T3/T7-like RNA polymerase sequences reported here are likely derived from genes encoding the mitochondrial RNA polymerase in the organisms in which they occur, suggesting a phage T3/T7-like RNA polymerase was recruited to act in transcription in the mitochondrion at an early stage in the evolution of this organelle.

• PMID: 8604305
• DOI full text
• PMC full text
• PubMed

Reference Type

Journal Article | Research Support, Non-U.S. Gov't

Authors

Cermakian N, Ikeda TM, Cedergren R, Gray MW

Primary Lit For

Additional Lit For

Review For