来自内生逆转录病毒的DNA是哺乳动物基因组中一个共同先祖特征。 此前，逆转录病毒一直是已知留下这种类型的一个化石记录的惟一一组病毒，但现在，来自Borna-like N (EBLN)序列的元素已在人类、非人类灵长目动物、啮齿类和一种黄鼠（地松鼠）的基因组中被发现。

Borna病毒（Bornaviruses）是未分段的、负链RNA病毒，在被感染细胞的细胞核中复制。在灵长目动物中，这些元素非常古老，是在距今超过4000万年前形成的，而松鼠EBLN序列产生的时间则较晚。灵长类EBLN的开放阅读框的保留，以及它们作为mRNA的表达，意味着它们在其宿主内可能发挥着基因新颖性之来源的功能。

原始出处：

Nature 463, 84-87 (7 January 2010) | doi:10.1038/nature08695

Endogenous non-retroviral RNA virus elements in mammalian genomes

Masayuki Horie1,7, Tomoyuki Honda1,2,7, Yoshiyuki Suzuki3, Yuki Kobayashi3, Takuji Daito1, Tatsuo Oshida4, Kazuyoshi Ikuta1, Patric Jern5, Takashi Gojobori3, John M. Coffin5 & Keizo Tomonaga1,6

1 Department of Virology, Research Institute for Microbial Diseases (BIKEN), Osaka University, Osaka 565-0871, Japan
2 Japan Society for the Promotion of Science (JSPS), Chiyoda-ku, Tokyo 102-8472, Japan
3 Center for Information Biology and DNA Data Bank of Japan, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan
4 Department of Life Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan
5 Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA
6 PRESTO, Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo 102-0075, Japan
7 These authors contributed equally to this work.

Retroviruses are the only group of viruses known to have left a fossil record, in the form of endogenous proviruses, and approximately 8% of the human genome is made up of these elements1, 2. Although many other viruses, including non-retroviral RNA viruses, are known to generate DNA forms of their own genomes during replication3, 4, 5, none has been found as DNA in the germline of animals. Bornaviruses, a genus of non-segmented, negative-sense RNA virus, are unique among RNA viruses in that they establish persistent infection in the cell nucleus6, 7, 8. Here we show that elements homologous to the nucleoprotein (N) gene of bornavirus exist in the genomes of several mammalian species, including humans, non-human primates, rodents and elephants. These sequences have been designated endogenous Borna-like N (EBLN) elements. Some of the primate EBLNs contain an intact open reading frame (ORF) and are expressed as mRNA. Phylogenetic analyses showed that EBLNs seem to have been generated by different insertional events in each specific animal family. Furthermore, the EBLN of a ground squirrel was formed by a recent integration event, whereas those in primates must have been formed more than 40 million years ago. We also show that the N mRNA of a current mammalian bornavirus, Borna disease virus (BDV), can form EBLN-like elements in the genomes of persistently infected cultured cells. Our results provide the first evidence for endogenization of non-retroviral virus-derived elements in mammalian genomes and give novel insights not only into generation of endogenous elements, but also into a role of bornavirus as a source of genetic novelty in its host.