title: Gene expression levels influence amino acid usage and evolutionary rates in endosymbiotic bacteria.
abstract: Most endosymbiotic bacteria have extremely reduced genomes, accelerated evolutionary rates, and strong AT base compositional bias thought to reflect reduced efficacy of selection and increased mutational pressure. Here, we present a comparative study of evolutionary forces shaping five fully sequenced bacterial endosymbionts of insects. The results of this study were three-fold: (i) Stronger conservation of high expression genes at not just nonsynonymous, but also synonymous, sites. (ii) Variation in amino acid usage strongly correlates with GC content and expression level of genes. This pattern is largely explained by greater conservation of high expression genes, leading to their higher GC content. However, we also found indication of selection favoring GC-rich amino acids that contrasts with former studies. (iii) Although the specific nutritional requirements of the insect host are known to affect gene content of endosymbionts, we found no detectable influence on substitution rates, amino acid usage, or codon usage of bacterial genes involved in host nutrition.
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de Valencia, A.C. 22085, 46071 Valencia, Spain. schaber@molgen.mpg.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Schaber
authors.forename: Claude
authors.initials: C
authors.lastname: Rispe
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wernegreen
authors.forename: Andreas
authors.initials: A
authors.lastname: Buness
authors.forename: François
authors.initials: F
authors.lastname: Delmotte
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Silva
authors.forename: Andrés
authors.initials: A
authors.lastname: Moya
mesh_terms: D020856:AT Rich Sequence / Q000235:genetics; D019943:Amino Acid Substitution / Q000235:genetics; D000596:Amino Acids / Q000235:genetics*; D000818:Animals; D001419:Bacteria / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D020635:Buchnera / Q000235:genetics; D003062:Codon / Q000235:genetics; D030561:Databases, Nucleic Acid; D019143:Evolution, Molecular; D020862:GC Rich Sequence / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D007313:Insecta / Q000382:microbiology; D009154:Mutation; D013045:Species Specificity; D013559:Symbiosis; D044106:Wigglesworthia / Q000235:genetics
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D003062:Codon