title: Extraordinary genome stability in the ciliate Paramecium tetraurelia.
abstract: 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.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405, USA. waysung@indiana.edu
authors.forename: Way
authors.initials: W
authors.lastname: Sung
authors.forename: Abraham E
authors.initials: AE
authors.lastname: Tucker
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Doak
authors.forename: Eunjin
authors.initials: E
authors.lastname: Choi
authors.forename: W Kelley
authors.initials: WK
authors.lastname: Thomas
authors.forename: Michael
authors.initials: M
authors.lastname: Lynch
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D018503:Genome, Protozoan / Q000235:genetics*; D042822:Genomic Instability / Q000235:genetics*; D008928:Mitochondria / Q000235:genetics; D059645:Mutation Rate; D016805:Paramecium tetraurelia / Q000201:enzymology / Q000235:genetics*; D012098:Reproduction / Q000235:genetics
chemical_list: D004259:DNA-Directed DNA Polymerase