全球最大的病毒拥有1000多个基因

近年来，随着分子生物学和生物信息学技术的不断发展，科学家对病毒的研究取得了突破性的进展。其中，一种名为“Megavirus chilensis”的巨型病毒引起了广泛关注。

这种病毒是在智利海域的一个研究站附近提取的海水样本中发现的。其基因组含有近126万个碱基对，是目前已知最大的DNA病毒。相比此前的纪录保持者——2003年分离出的拟菌病毒，其个头大了6.5%。

有趣的是，这种病毒与细菌不同，它们的个头往往更小，同时无法自行繁殖，需要进入宿主细胞内进行繁殖。这种特性使得科学家对这种巨型病毒的宿主和感染机制产生了浓厚的兴趣。

目前，研究人员还不确定这种病毒为何拥有如此大的个头。一种假设认为，随着时间的流逝，M. chilensis病毒不断“偷盗”前宿主的DNA，这一过程被称之为“基因转移”。另一种观点认为，M. chilensis病毒和拟菌病毒源自一个更为复杂的祖先，继承了祖先的细胞基因组。

克拉维莱教授表示，DNA病毒包括痘病毒和疱疹病毒，M. chilensis似乎对人体无害。在本周出版的美国《国家科学院院刊》上，研究人员对这种病毒进行了描述。

Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae

Arslan， Defne; Legendre, Matthieu; Seltzer, Virginie; Abergel, Chantal; Claverie, Jean-Michel

Mimivirus, a DNA virus infecting acanthamoeba, was for a long time the largest known virus both in terms of particle size and gene content. Its genome encodes 979 proteins, including the first four aminoacyl tRNA synthetases (ArgRS, CysRS, MetRS, and TyrRS) ever found outside of cellular organisms. The discovery that Mimivirus encoded trademark cellular functions prompted a wealth of theoretical studies revisiting the concept of virus and associated large DNA viruses with the emergence of early eukaryotes. However, the evolutionary significance of these unique features remained impossible to assess in absence of a Mimivirus relative exhibiting a suitable evolutionary divergence. Here, we present Megavirus chilensis, a giant virus isolated off the coast of Chile, but capable of replicating in fresh water acanthamoeba. Its 1,259,197-bp genome is the largest viral genome fully sequenced so far. It encodes 1,120 putative proteins, of which 258 (23%) have no Mimivirus homologs. The 594 Megavirus/Mimivirus orthologs share an average of 50% of identical residues. Despite this divergence, Megavirus retained all of the genomic features characteristic of Mimivirus, including its cellular-like genes. Moreover, Megavirus exhibits three additional aminoacyl-tRNA synthetase genes (IleRS, TrpRS, and AsnRS) adding strong support to the previous suggestion that the Mimivirus/Megavirus lineage evolved from an ancestral cellular genome by reductive evolution. The main differences in gene content between Mimivirus and Megavirus genomes are due to (i) lineages specific gains or losses of genes, (ii) lineage specific gene family expansion or deletion, and (iii) the insertion/migration of mobile elements (intron, intein).