Legendre Matthieu, Arslan Defne, Abergel Chantal, Claverie Jean-Michel
Information Génomique et Structurale; Centre National de la Recherche Scientifique-Unité Propre de Recherche 2589; Aix-Marseille University; Institut de Microbiologie de la Méditerranée; Parc Scientifique de Luminy; Case 934; Marseille, France.
Commun Integr Biol. 2012 Jan 1;5(1):102-6. doi: 10.4161/cib.18624.
We recently described Megavirus chilensis, a giant virus isolated off the coast of Chile, also replicating in fresh water acanthamoeba. Its 1,259,197-bp genome encodes 1,120 proteins and is the largest known viral genome. Megavirus and its closest relative Mimivirus only share 594 orthologous genes, themselves sharing only 50% of identical residues in average. Despite this divergence, comparable to the maximal divergence exhibited by bacteria within the same division (e.g., gamma proteobacteria), Megavirus retained all of the genomic features unique to Mimivirus, in particular its genes encoding key-elements of the translation apparatus, a trademark of cellular organisms. Besides homologs to the four aminoacyl-tRNA synthetases (aaRS) encoded by Mimivirus, Megavirus added three additional ones, raising the total of known virus-encoded aaRS to seven: IleRS, TrpRS, AsnRS, ArgRS, CysRS, MetRS, TyrRS. This finding strongly suggests that large DNA viruses derived from an ancestral cellular genome by reductive evolution. The nature of this cellular ancestor remains hotly debated.
我们最近描述了智利沿海分离出的一种巨型病毒——智利梅加病毒，它也能在淡水棘阿米巴中复制。其1,259,197碱基对的基因组编码1,120种蛋白质，是已知最大的病毒基因组。梅加病毒及其最亲近的亲戚米米病毒仅共享594个直系同源基因，它们平均仅共享50%的相同残基。尽管存在这种差异，这与同一分类内细菌所表现出的最大差异相当（例如γ-变形菌纲），但梅加病毒保留了米米病毒特有的所有基因组特征，特别是其编码翻译装置关键元件的基因，这是细胞生物的一个标志。除了与米米病毒编码的四种氨酰-tRNA合成酶（aaRS）的同源物外，梅加病毒还增加了另外三种，使已知病毒编码的aaRS总数达到七种：异亮氨酰-tRNA合成酶、色氨酰-tRNA合成酶、天冬氨酰-tRNA合成酶、精氨酰-tRNA合成酶、半胱氨酰-tRNA合成酶、甲硫氨酰-tRNA合成酶、酪氨酰-tRNA合成酶。这一发现有力地表明，大型DNA病毒是通过简化进化从祖先细胞基因组衍生而来的。这种细胞祖先的本质仍存在激烈争论。
