Extraordinary genome stability in the ciliate Paramecium tetraurelia

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 47; pp. 19339 - 19344
• Main Authors: Sung, Way, Tucker, Abraham E, Doak, Thomas G, Choi, Eunjin, Thomas, W. Kelley, Lynch, Michael
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 20.11.2012; National Acad Sciences
• Subjects: Amino Acid Substitution - genetics; Amino acids; Autogamy; Biological Sciences; Cell division; Cell lines; DNA; DNA-Directed DNA Polymerase - metabolism; Eukaryotes; Eukaryotic cells; Evolution; Gene expression; genetic disorders; Genetic drift; Genetic mutation; genome; Genome, Protozoan - genetics; Genomes; Genomic Instability - genetics; Germ cells; Mitochondria - genetics; Mutation; Mutation Rate; natural selection; Paramecium tetraurelia; Paramecium tetraurelia - enzymology; Paramecium tetraurelia - genetics; Reproduction - genetics; transcription (genetics)
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1210663109

Mutation plays a central role in all evolutionary processes and is also the basis of genetic disorders. Established base-substitution mutation rates in eukaryotes range between ∼5 × 10 ⁻¹⁰ and 5 × 10 ⁻⁸ per site per generation, but here we report a genome-wide estimate for Paramecium tetraurelia that is more than an order of magnitude lower than any previous eukaryotic estimate. Nevertheless, when the mutation rate per cell division is extrapolated to the length of the sexual cycle for this protist, the measure obtained is comparable to that for multicellular species with similar genome sizes. Because Paramecium has a transcriptionally silent germ-line nucleus, these results are consistent with the hypothesis that natural selection operates on the cumulative germ-line replication fidelity per episode of somatic gene expression, with the germ-line mutation rate per cell division evolving downward to the lower barrier imposed by random genetic drift. We observe ciliate-specific modifications of widely conserved amino acid sites in DNA polymerases as one potential explanation for unusually high levels of replication fidelity.