Some friendly, some not so.-http://www.the-scientist.com/?articles.view/articleNo/41989/title/Viral-Virtuosos/-"Persistent viruses may play roles both in defending their hosts—they have been speculated to “tune” our immune response, priming it to better combat more harmful microbes—and in directly causing serious disease in humans. This double-edged sword of viral persistence makes the phenomenon all the more important to understand. Elucidating how miRNAs and other ncRNAs function could spawn new therapies, while yielding insights about the evolutionary forces that dictate parasitism, mutualism, and other multiorganismal relationships.-"In most eukaryotes, RNAi defends the host against mobile genetic elements such as endogenous transposons, and in some organisms, such as plants and insects, against viruses. In these organisms, foreign viral RNA is recognized and destroyed by a series of host machineries. Whether or not RNAi also serves as a meaningful antiviral response in mammals remains a controversial and unresolved issue.3,4 What is clear, however, is that multicellular eukaryotes, including mammals, generate endogenous miRNAs that enter the RNAi machinery to silence specific mRNAs, thus providing an additional layer of control for gene expression.-"Over the last decade, my lab and several others have uncovered virus-encoded miRNAs from diverse viruses.5,6 This provides an interesting twist—host machinery that serves as an antiviral response in many organisms has been usurped by viruses for their own benefit. By binding to and silencing viral transcripts, for example, or by targeting host genes important for viral gene expression, viral miRNAs can optimize the location and timing of virus replication to fly under the radar of the host immune response. Some viruses also utilize miRNAs to directly regulate host defenses."