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Gene silencing is the process of "turning off" a gene, thereby preventing it from expressing in the form of protein production or other forms of expression. This process happens naturally in many cases for the purpose of regulating the expression of genes and preventing potential damage from viruses. Gene silencing is also an important laboratory technique, as disabling a gene is a highly effective way of determining the purpose of that gene. A gene may be silenced in a variety of different ways and through one of many different mechanisms — there is not just one way to prevent gene expression. It should be noted that silencing does not occur as a result of modification or damage to the gene itself — the gene remains intact and outside mechanisms prevent its expression.
Gene expression occurs when deoxyribonucleic acid (DNA) is converted to ribonucleic acid (RNA) through a process called transcription. The RNA is then converted to proteins, the primary functional units in cells that are involved in almost all cellular processes, through a process called translation. This process can occur at a transcriptional or a post-transcriptional level, meaning that it can interfere with the process of transcription or with some later process that leads to gene expression. The gene itself is not affected, but the various steps that lead up to expression are not allowed to run to completion.
There are many different transcriptional and post-transcriptional processes that can lead to gene silencing. One transcriptional gene silencing process is referred to as DNA methylation. Methylation involves attaching a methyl group to certain points on a nucleic acid strand and can, based on the circumstances, have a variety of different effects, some of which prevent transcription. RNA interference, or RNAi, is a common method of post-transcriptional gene silencing. In RNAi, small RNA molecules enter into a protein complex that cleaves specific RNA strands, preventing them from being translated to protein, thereby preventing gene expression.
RNAi and other methods are commonly used in biology laboratories to induce the process for the purpose of studying the effects of various genes. Disabling a gene and observing the changes is one valuable way to determine the exact purpose of a given gene. If, for instance, silencing a gene results in organisms without eye pigmentation, one can be reasonably confident that that gene has something to do with eye pigmentation. In many cases, however, laboratory gene silencing kills the organism of interest or causes no noticeable effect, making further research necessary.
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