RNA interference (RNAi) or double-stranded RNA (dsRNA) is a system within living cells that help control which genes are active and their activity level. siRNAs were first discovered by David Baulcombe's group in Norwich, England, as part of post-transcriptional gene silencing (PTGS) in plants1 and later independently identified in a wide variety of eukaryotic organisms. These dsRNAs are rapidly processed into short RNA duplexes of 21 to 28 nucleotides in length, which in turn guides the recognition and ultimately the division of complementary single-stranded RNA such as messenger RNAs or viral genomic / antigenomic RNA (Fig. 1). According to their source or function, a native of small RNAs have been described: short interfering RNAs (siRNAs), repeat-associated short interfering RNA (siRNA or rasiRNA) and microRNA (miRNA). RNA interference has many biological functions - is a vital part of the immune response against the virus, and downregulates gene expression by transcriptional silencing of genes or activation upregulates the promotion of RNA. Finally, the artificial introduction of long dsRNA or siRNA has been adopted as a tool to inactivate gene expression in both cultured cells and in living organisms.
A biochemical understanding of the RNAi pathway was crucial to realize that dsRNAs less than 30 base pairs (bp) could be used to trigger a response by RNAi in mammals. Tuschl and colleagues showed that transfection of mammalian cells with short RNA could lead to the path of the sequence-specific RNAi, for surpassing the barrier to the use of RNAi as a genetic tool in mammals2. The impulse to use siRNAs and other small RNAs in mammalian cells also came from the long view that the receptor protein kinase (PKR) activation3 and similar responses were not caused by short dsRNAs effectively. Following initial reports, took a very short period of time for active siRNAs to be adopted as a standard component of the toolbox of molecular biology. siRNAs can be introduced into mammalian cells using a variety of standard transfection methods. The strength and duration of the silencing response is determined by several factors: a population base, the response of silencing is affected mainly by the overall efficiency of transfection, which can be addressed by optimizing the conditions. In each cell, silencing depends on the amount of siRNA that is delivered and the potential of each siRNA to suppress its target, or power. Even a relatively powerless siRNA can silence its target, provided that sufficient amounts of siRNA delivered. However, essentially "forcing" the system by providing large amounts of reagents can give rise to many undesirable effects.
A biochemical understanding of the RNAi pathway was crucial to realize that dsRNAs less than 30 base pairs (bp) could be used to trigger a response by RNAi in mammals. Tuschl and colleagues showed that transfection of mammalian cells with short RNA could lead to the path of the sequence-specific RNAi, for surpassing the barrier to the use of RNAi as a genetic tool in mammals2. The impulse to use siRNAs and other small RNAs in mammalian cells also came from the long view that the receptor protein kinase (PKR) activation3 and similar responses were not caused by short dsRNAs effectively. Following initial reports, took a very short period of time for active siRNAs to be adopted as a standard component of the toolbox of molecular biology. siRNAs can be introduced into mammalian cells using a variety of standard transfection methods. The strength and duration of the silencing response is determined by several factors: a population base, the response of silencing is affected mainly by the overall efficiency of transfection, which can be addressed by optimizing the conditions. In each cell, silencing depends on the amount of siRNA that is delivered and the potential of each siRNA to suppress its target, or power. Even a relatively powerless siRNA can silence its target, provided that sufficient amounts of siRNA delivered. However, essentially "forcing" the system by providing large amounts of reagents can give rise to many undesirable effects.
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