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Giant viruses with an expanded complement of translation system components

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Science  07 Apr 2017:
Vol. 356, Issue 6333, pp. 82-85
DOI: 10.1126/science.aal4657

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The evolution of giant virus genomes

Some giant viruses encode a genome larger than that of some bacteria, but their evolutionary history is a mystery. Examining the genomes within a sample from a wastewater treatment plant in Austria, Schulz et al. assembled a previously undiscovered giant virus genome, which they used to mine genetic databases for related viruses. The authors thus identified a group of giant viruses with more genes encoding components of the protein translation machinery, including aminoacyl transfer RNA synthetases, than in other giant viruses. Phylogenetic analyses suggest that the genes were acquired in an evolutionarily recent time frame, likely from, and as an adaptation to, their hosts.

Science, this issue p. 82

Abstract

The discovery of giant viruses blurred the sharp division between viruses and cellular life. Giant virus genomes encode proteins considered as signatures of cellular organisms, particularly translation system components, prompting hypotheses that these viruses derived from a fourth domain of cellular life. Here we report the discovery of a group of giant viruses (Klosneuviruses) in metagenomic data. Compared with other giant viruses, the Klosneuviruses encode an expanded translation machinery, including aminoacyl transfer RNA synthetases with specificities for all 20 amino acids. Notwithstanding the prevalence of translation system components, comprehensive phylogenomic analysis of these genes indicates that Klosneuviruses did not evolve from a cellular ancestor but rather are derived from a much smaller virus through extensive gain of host genes.

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