Virophages are satellite DNA viruses that depend for their replication on giant viruses of the family Mimiviridae. An evolutionary relationship exists between the virophages and Polintons, large self-synthesizing transposons that are wide spread in the genomes of diverse eukaryotes. Most of the Polintons encode homologs of major and minor icosahedral virus capsid proteins and accordingly are predicted to form virions. Additionally, metagenome analysis has led to the discovery of an expansive family of Polinton-like viruses (PLV) that are more distantly related to bona fide Polintons and virophages. Another group of giant virus parasites includes small, linear, double-stranded DNA elements called transpovirons. Recent in-depth comparative genomic analysis has yielded evidence of the origin of the PLV and the transpovirons from Polintons. Integration of virophage genomes into genomes of both giant viruses and protists has been demonstrated. Furthermore, in an experimental coinfection system that consisted of a protist host, a giant virus and an associated virophage, the virophage integrated into the host genome and, after activation of its expression by a superinfecting giant virus, served as an agent of adaptive immunity. There is a striking analogy between this mechanism and the CRISPR-Cas system of prokaryotic adaptive immunity. Taken together, these findings show that Polintons, PLV, virophages and transpovirons form a dynamic network of integrating mobile genetic elements that contribute to the cellular antivirus defense and host–virus coevolution.

噬菌体是卫星DNA病毒，它们依赖于Mimiviridae家族的巨型病毒进行复制。噬菌体和Polinton之间存在着进化关系，Pinintons是在各种真核生物的基因组中广泛分布的大型自合成转座子。大多数回弹蛋白编码主要和次要二十面体病毒衣壳蛋白的同源物，因此据预测会形成病毒体。此外，宏基因组分析导致了一个广阔的家人发现Polinton，这样更远亲病毒（PLV）善意蛋卷和病毒体。另一类巨大的病毒寄生虫包括小的，线性，双链DNA元素，称为转座病毒子。最近的深入比较基因组分析已提供了PLV和来自Polintons的转座病毒的起源的证据。已证明将噬菌体基因组整合到巨型病毒和原生生物的基因组中。此外，在由原生生物宿主，巨型病毒和相关的病毒噬菌体组成的实验性共感染系统中，该病毒噬菌体整合到宿主基因组中，并在被超级感染的巨型病毒激活表达后用作适应性免疫的媒介。在该机制与原核适应性免疫的CRISPR-Cas系统之间有一个惊人的类比。综上所述，这些发现表明Polintons，PLV，