- RNAa
Small double-stranded RNA (dsRNA) has been found to silence gene expression by an evolutionally conserved mechanism known as
RNA interference orRNAi . Such dsRNAs are called small interfering RNAs orsiRNA . RNAi can occur at both transcriptional and post-transcriptional levels. Surprisingly, two recent studies have found that dsRNA can also activate gene expression, a mechanism that has been termed "small RNA-induced gene activation" or RNAa.Li LC, et al. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17085592&query_hl=1&itool=pubmed_docsum Small dsRNAs induce transcriptional activation in human cells. Proc Natl Acad Sci U S A. 2006 Nov 14;103(46):17337-42. [Epub 2006 Nov 3.] ] ] Janowski BA, et al. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=17259978&query_hl=2&itool=pubmed_docsum Activating gene expression in mammalian cells with promoter-targeted duplex RNAs. Nat Chem Biol. 2007 Jan 28; [Epub ahead of print] ] ] cite book |chapterurl=http://www.horizonpress.com/rnareg|author= Li LC|year=2008|chapter=Small RNA-Mediated Gene Activation|title=RNA and the Regulation of Gene Expression: A Hidden Layer of Complexity|publisher=Caister Academic Press|id= [http://www.horizonpress.com/rnareg ISBN 978-1-904455-25-7] ] It has been shown that dsRNAs targeting gene promoters induce potent transcriptional activation of associated genes. Both studies demonstrate RNAa in human cells using synthetic dsRNAs termed small activating RNAs (saRNA s). Endogenous miRNA that cause RNAa has also been found in humans. [cite journal | author=Check E| title=RNA interference: hitting the on switch| journal=Nature| year=2007| volume=448| issue=7156| pages=855–858| pmid=17713502| doi=10.1038/448855a] It is currently unknown if RNAa is conserved in other organisms.Another surprising observation is that gene activation by RNAa is long-lasting. Induction of gene expression has been seen to last for over ten days. The prolonged effect of RNAa could be attributed to
epigenetic changes at dsRNA target sites.References
Further reading
*Morris KV (2008). [http://www.horizonpress.com/rnareg RNA and the Regulation of Gene Expression: A Hidden Layer of Complexity] . Caister Academic Press [http://www.horizonpress.com/rnareg ISBN 978-1-904455-25-7]
*Tost J (2008). [http://www.horizonpress.com/epi Epigenetics] . Caister Academic Press [http://www.horizonpress.com/epi ISBN 978-1-904455-23-3]External links
*Small RNAs Reveal an Activating Side. [http://www.sciencemag.org/cgi/content/full/314/5800/741a Science News of the Week]
*How to get your genes switched on. [http://www.newscientist.com/channel/life/genetics/mg19225780.149-how-to-get-your-genes-switched-on.html New Scientist 16 November 2006]
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