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Báo cáo y học: " Ubiquitous RNA-dependent RNA polymerase and gene silencing"

Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Ubiquitous RNA-dependent RNA polymerase and gene silencing. | X Genome Biology Minireview Ubiquitous RNA-dependent RNA polymerase and gene silencing James A Birchler Address Division of Biological Sciences University of Missouri Columbia MO 65211 USA. Email BirchlerJ@Missouri.edu Abstract The discovery of a novel RNA-dependent RNA polymerase activity with a eukaryote-wide distribution raises new questions about the roles and mechanisms of gene silencing by small RNAs. The phenomenon of the silencing of transgenes together with homologous genes in the host genome was first discovered some two decades ago in plants 1-3 . This silencing was eventually found to involve either post-transcriptional destruction of the transgene mRNAs 2 3 or prevention of their transcription 1 . The biological rationale for these processes was proposed to be a defense against viruses and transposable elements. Doublestranded RNA dsRNA is a target of the silencing mechanism and many viruses produce such RNA as part of their life cycle. Similarly transposable elements produce aberrant RNAs that enter the silencing pathway and this prevents transposition. This host defense concept has since been supported by a wide variety of evidence. The independent discovery in Caenorhabditis elegans that introduced sense RNAs could cause gene silencing led to the development of the technique of RNA interference RNAi 4 . The finding that the active ingredient in triggering RNAi was a dsRNA ignited a revolution in genetics that continues to this day 5 . An interesting aspect of post-transcriptional silencing in plants and worms is that silencing can spread throughout the organism from the site of introduction of the dsRNA. This spread depends on the activity of an RNA-dependent RNA polymerase RdRP which amplifies dsRNA to produce more copies which are then cleaved by the enzyme Dicer to produce small interfering RNAs siRNAs 6 that target mRNAs of similar sequence for destruction. The genomes of Drosophila and mammals show no evidence of such an RdRP and the spread of