have been uncovered. It is trusted that the miRNAs can direct negative or positive regulation at different levels, which depends on the specific miRNAs and target base pair interaction and the cofactors that recognize them. Because it has been widely known that many viruses have RNA rather than DNA as their genetic material and go through at least one stage in their life cycle when they make double-stranded RNA, RNA interference has been considered to be a potentially evolutionarily ancient mechanism for protecting organisms from viruses. The small interfering RNAs produced by Dicer cause sequence specific, post-transcriptional gene silencing by guiding an endonuclease, the RNA-induced silencing complex (RISC), to mRNA. This process has been seen in a wide range of organisms, such as Neurospora fungus (in which it is known as quelling), plants (post-transcriptional gene silencing) and mammalian cells(RNAi). If there is a complete or near complete sequence complementarity between the small RNA and the target, the Argonaute protein component of RISC mediates cleavage of the target transcript, the mechanism involves repression of translation predominantly. Importantly, Argonaute 4 (AGO4)-deficient influenza-infected mice have significantly higher burden and viral titers in vivo which is in contrast to AGO1 or AGO3-deficient mice. So, specific promotion of AGO4 function in mammalian cells may be an effective antiviral strategy. Biotechnological applications of prokaryotic Argonaute proteins In 2016, a group from Hebei University of Science and Technology reported genome editing using a prokaryotic Argonaute protein from Natronobacterium gregoryi. However, evidence for application of Argonaute proteins as DNA-guided nucleases for genome editing have been questioned, with the retraction of the claim from the leading journal. In 2017, a group from University of Illinois reported using a prokaryotic Argonaute protein taken from Pyrococcus furiosus (PfAgo) along with guide DNA to edit DNA in vitro'' as artificial restriction enzymes. PfAgo based artificial restriction enzymes were also used for storing data on native DNA sequences via enzymatic nicking. References External links starBase database: a database for exploring microRNA–mRNA interaction maps from Argonaute CLIP-Seq(HITS-CLIP, PAR-CLIP) and Degradome-Seq data. Ribonucleases Molecular genetics MicroRNA RNA-binding proteins RNA interference