Gene silencing stops a gene being expressed, usually by preventing its mRNA from being translated into protein. The gene itself is not removed.RNA interference (RNAi)
The main method is RNA interference, a natural process that cells use to control genes and to defend against viruses.
1. A double-stranded RNA molecule with the same sequence as part of the target gene is introduced into the cell.
2. An enzyme called Dicer cuts it into short pieces about 21 to 23 nucleotides long, called small interfering RNA (siRNA).
3. One strand of each siRNA joins a protein complex called RISC (RNA-induced silencing complex).
4. The siRNA binds to any mRNA with a complementary base sequence.
5. RISC cuts the mRNA, which is then broken down, so no protein is made.MicroRNAs (miRNAs) are made by the cell's own genes and work in a similar way, often blocking translation rather than cutting the mRNA.Antisense RNA is an older method: a single RNA strand complementary to the mRNA binds to it and blocks translation.Uses
• Research: silencing a gene and observing how the phenotype changes shows what the gene does.
• Crops: the first GM tomato had a softening enzyme gene silenced by antisense RNA, so it stayed firm for longer.
• Medicine: siRNA drugs are approved to silence faulty genes, for example in a form of inherited amyloidosis, and could be used against viruses or cancer genes.
The main method is RNA interference, a natural process that cells use to control genes and to defend against viruses.
1. A double-stranded RNA molecule with the same sequence as part of the target gene is introduced into the cell.
2. An enzyme called Dicer cuts it into short pieces about 21 to 23 nucleotides long, called small interfering RNA (siRNA).
3. One strand of each siRNA joins a protein complex called RISC (RNA-induced silencing complex).
4. The siRNA binds to any mRNA with a complementary base sequence.
5. RISC cuts the mRNA, which is then broken down, so no protein is made.MicroRNAs (miRNAs) are made by the cell's own genes and work in a similar way, often blocking translation rather than cutting the mRNA.Antisense RNA is an older method: a single RNA strand complementary to the mRNA binds to it and blocks translation.Uses
• Research: silencing a gene and observing how the phenotype changes shows what the gene does.
• Crops: the first GM tomato had a softening enzyme gene silenced by antisense RNA, so it stayed firm for longer.
• Medicine: siRNA drugs are approved to silence faulty genes, for example in a form of inherited amyloidosis, and could be used against viruses or cancer genes.