“巨病毒”（giant virus）分离毒株来自英国Bradford的一个冷却塔。最初因其大小（是最大已知病毒的三倍大，而且大于很多细菌）该病毒被误为一种细菌，它是在名为“Acanthamoeba polyphaga”的原生动物中发现的。当它被识别为一种病毒时，它被称之为一种模仿病毒（mimivirus，因其与细菌相似而得名），正式称谓为APMV (Acanthamoeba polyphaga mimivirus)。
现在，一种新的、甚至更大的APMV毒株（名为“mamavirus”）已从巴黎一个水冷却塔中分离出来。引人注目的是，该病毒并不是孤立的，其本身还被一种“卫星病毒”（satellite virus）所寄生。被称为Sputnik的这种病毒在“建造”在被APMV共感染的阿米巴中的“病毒工厂”中复制。比照噬菌体，Sputnik被看作是人们所发现的第一种噬病毒体（virophage）。它也许只是一座噬病毒体冰山之一角，因为对海洋水域所进行的宏基因组学研究显示，存在大量与巨病毒密切相关的基因序列，从而导致人们怀疑：它们是一种共同的浮游生物寄生虫。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 455, 100-104 (4 September 2008) | doi:10.1038/nature07218
The virophage as a unique parasite of the giant mimivirus
Bernard La Scola1,6, Christelle Desnues1,6, Isabelle Pagnier1, Catherine Robert1, Lina Barrassi1, Ghislain Fournous1, Michèle Merchat2, Marie Suzan-Monti1, Patrick Forterre3,4, Eugene Koonin5 & Didier Raoult1
Viruses are obligate parasites of Eukarya, Archaea and Bacteria.Acanthamoeba polyphaga mimivirus (APMV) is the largest known virus; it grows only in amoeba and is visible under the optical microscope. Mimivirus possesses a 1,185-kilobase double-stranded linear chromosome whose coding capacity is greater than that of numerous bacteria and archaea1, 2, 3. Here we describe an icosahedral small virus, Sputnik, 50 nm in size, found associated with a new strain of APMV. Sputnik cannot multiply in Acanthamoeba castellanii but grows rapidly, after an eclipse phase, in the giant virus factory found in amoebae co-infected with APMV4. Sputnik growth is deleterious to APMV and results in the production of abortive forms and abnormal capsid assembly of the host virus. The Sputnik genome is an 18.343-kilobase circular double-stranded DNA and contains genes that are linked to viruses infecting each of the three domains of life Eukarya, Archaea and Bacteria. Of the 21 predicted protein-coding genes, eight encode proteins with detectable homologues, including three proteins apparently derived from APMV, a homologue of an archaeal virus integrase, a predicted primase–helicase, a packaging ATPase with homologues in bacteriophages and eukaryotic viruses, a distant homologue of bacterial insertion sequence transposase DNA-binding subunit, and a Zn-ribbon protein. The closest homologues of the last four of these proteins were detected in the Global Ocean Survey environmental data set5, suggesting that Sputnik represents a currently unknown family of viruses. Considering its functional analogy with bacteriophages, we classify this virus as a virophage. The virophage could be a vehicle mediating lateral gene transfer between giant viruses.
