Intraphylum diversity and complex evolution of cyanobacterial aminoacyl-tRNA synthetases.

A comparative genomic analysis of 35 cyanobacterial strains has revealed that the gene complement of aminoacyl-tRNA synthetases (AARSs) and routes for aminoacyl-tRNA synthesis may differ among the species of this phylum. Several genes encoding AARS paralogues were identified in some genomes. In-depth phylogenetic analysis was done for each of these proteins to gain insight into their evolutionary history. GluRS, HisRS, ArgRS, ThrRS, CysRS, and Glu-Q-RS showed evidence of a complex evolutionary course as indicated by a number of inconsistencies with our reference tree for cyanobacterial phylogeny. In addition to sequence data, support for evolutionary hypotheses involving horizontal gene transfer or gene duplication events was obtained from other observations including biased sequence conservation, the presence of indels (insertions or deletions), or vestigial traces of ancestral redundant genes. We present evidences for a novel protein domain with two putative transmembrane helices recruited independently by distinct AARS in particular cyanobacteria.