title: Drift Barriers to Quality Control When Genes Are Expressed at Different Levels.
abstract: Gene expression is imperfect, sometimes leading to toxic products. Solutions take two forms: globally reducing error rates, or ensuring that the consequences of erroneous expression are relatively harmless. The latter is optimal, but because it must evolve independently at so many loci, it is subject to a stringent "drift barrier"-a limit to how weak the effects of a deleterious mutation s can be, while still being effectively purged by selection, expressed in terms of the population size N of an idealized population such that purging requires s < -1/N In previous work, only large populations evolved the optimal local solution, small populations instead evolved globally low error rates, and intermediate populations were bistable, with either solution possible. Here, we take into consideration the fact that the effectiveness of purging varies among loci, because of variation in gene expression level, and variation in the intrinsic vulnerabilities of different gene products to error. The previously found dichotomy between the two kinds of solution breaks down, replaced by a gradual transition as a function of population size. In the extreme case of a small enough population, selection fails to maintain even the global solution against deleterious mutations, explaining the nonmonotonic relationship between effective population size and transcriptional error rate that was recently observed in experiments on Escherichia coli, Caenorhabditis elegans, and Buchnera aphidicola.
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85721.
authors.forename: Kun
authors.identifier: 0000-0003-1431-6586
authors.initials: K
authors.lastname: Xiong
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721.
authors.forename: Jay P
authors.identifier: 0000-0002-1213-9734
authors.initials: JP
authors.lastname: McEntee
authors.affiliation: Department of Computer Science, University of Arizona, Tucson, Arizona 85721.
authors.forename: David J
authors.identifier: 0000-0001-5383-3266
authors.initials: DJ
authors.lastname: Porfirio
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721 masel@emailarizona.edu.
authors.forename: Joanna
authors.identifier: 0000-0002-7398-2127
authors.initials: J
authors.lastname: Masel
mesh_terms: D000818:Animals; D005075:Biological Evolution; D020635:Buchnera / Q000235:genetics; D017173:Caenorhabditis elegans / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D019143:Evolution, Molecular; D015870:Gene Expression; D040961:Genetic Drift; D008957:Models, Genetic; D015233:Models, Statistical; D009154:Mutation; D011156:Population Density; D012641:Selection, Genetic; D014157:Transcription Factors / Q000235:genetics
chemical_list: D014157:Transcription Factors
keywords: cryptic genetic variation; evolvability; proofreading; robustness; stop codon readthrough; transcriptional errors