Pokusaeva, Victoria O.Usmanova, Dinara R.Putintseva, Ekaterina V.Espinar, LorenaSarkisyan, Karen S.Mishin, Alexander S.Bogatyreva, Natalya S.Ivankov, Dmitry N.Akopyan, Arseniy V.Avvakumov, Sergey YaPovolotskaya, Inna, 1986-Filion, GuillaumeCarey, Lucas, 1980-Kondrashov, Fyodor A., 1979-2019-06-072019-06-072019Pokusaeva VO, Usmanova DR, Putintseva EV, Espinar L, Sarkisyan KS, Mishin AS et al. An experimental assay of the interactions of amino acids from orthologous sequences shaping a complex fitness landscape. PLoS Genet. 2019;15(4):e1008079. DOI: 10.1371/journal.pgen.10080791553-7390http://hdl.handle.net/10230/41720Characterizing the fitness landscape, a representation of fitness for a large set of genotypes, is key to understanding how genetic information is interpreted to create functional organisms. Here we determined the evolutionarily-relevant segment of the fitness landscape of His3, a gene coding for an enzyme in the histidine synthesis pathway, focusing on combinations of amino acid states found at orthologous sites of extant species. Just 15% of amino acids found in yeast His3 orthologues were always neutral while the impact on fitness of the remaining 85% depended on the genetic background. Furthermore, at 67% of sites, amino acid replacements were under sign epistasis, having both strongly positive and negative effect in different genetic backgrounds. 46% of sites were under reciprocal sign epistasis. The fitness impact of amino acid replacements was influenced by only a few genetic backgrounds but involved interaction of multiple sites, shaping a rugged fitness landscape in which many of the shortest paths between highly fit genotypes are inaccessible.application/pdfeng© 2019 Pokusaeva et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.info:eu-repo/semantics/articlehttp://dx.doi.org/10.1371/journal.pgen.1008079Fitness epistasisAmino acid substitutionSaccharomyces cerevisiaeEpistasisSign epistasisProtein sequencingEvolutionary geneticsVariant genotypesinfo:eu-repo/semantics/openAccess