RNA interference

Your cells have a special way to stay safe.

They can stop bad things from growing. They use tiny bits of air-like parts to do this. This helps the cell work right.

First, a tiny tool cuts long parts into short bits.

These short bits act like a guide. They lead the cell to a target.

Once the guide finds the target, it stops it. This stops the cell from making a certain part. It is like a tiny shield for you.

This process helps cells fight off germs. It also helps living things grow.

Scientists use this to study how cells work. It can even help make medicine. It is a very smart way for cells to work.

Cells have a way to turn off certain genes. This is called RNA interference, or RNAi.

It helps cells defend against viruses. It also helps living things grow.

This way starts with long, double-stranded RNA. A tool called Dicer cuts these into short pieces.

These small pieces are called siRNAs. The siRNA then splits into two single strands. One strand is the passenger. The other is the guide strand.

The guide strand joins a group called RISC.

This group uses a protein called Argonaute to work. The guide strand leads RISC to a target mRNA. The mRNA is a part that tells the cell how to make proteins. When the guide finds its match, Argonaute cuts the mRNA. This stops the cell from making that protein.

There is another type of small RNA called miRNA. These also help control how genes work. Scientists use RNAi to study how cells divide. It can also be used to make new medicines. It is a very precise way to study life.

Cells have a way to turn off certain genes. This is called RNA interference, or RNAi.

It is a natural process found in many living things. RNAi helps cells defend against tiny invaders like viruses. It also helps organisms grow and develop correctly. Scientists now know that RNAi is a very precise and stable way to control genes. It is even better than some older methods used in medicine. This makes it a very important tool for understanding how life works.

The way it works starts with long, double-stranded RNA.

An enzyme called Dicer acts like a pair of molecular scissors. It cuts the long RNA into short fragments called siRNAs. These pieces are usually 21 to 23 nucleotides long. Next, the siRNA splits into two single strands. One is called the passenger strand and the other is the guide strand.

The passenger strand is removed by a protein called Argonaute 2. The guide strand then joins a group called the RNA-induced silencing complex, or RISC.

Once the RISC is ready, it can find its target. The guide strand leads the RISC to a matching piece of mRNA. mRNA is a molecule that carries instructions for making proteins. When the guide strand finds its perfect match, the Argonaute protein cuts the mRNA. This prevents the cell from using that mRNA to make a protein.

There is also another type of molecule called miRNA. These can also join the RISC to block proteins from being made. This helps the cell regulate many different things at once.

People first discovered the details of this process through careful study. Researchers Andrew Fire and Craig Mello studied a tiny worm called Caenorhabditis elegans. They published their important findings in 1998. Their work was so significant that they won the Nobel Prize in 2006.

Before this discovery, people used different names for this process. They called it things like quelling or post-transcriptional gene silencing. Now, we know all those names describe the same amazing thing.

Today, RNAi is used in many different ways. Scientists use it in labs to study how cells divide. It can even be used to create new medicines or better insecticides.

It is also a helpful tool for improving food. In the human body, RNAi helps keep our genes in balance. If this process does not work right, it might be linked to illnesses like cancer. It can also be connected to brain disorders like autism or Alzheimer's disease. This shows just how much RNAi matters to our health.

RNA interference, or RNAi, is a biological mechanism used to suppress gene expression. This process involves RNA molecules that stop specific genes from working. It can happen through transcriptional repression, which stops DNA from being read. It can also happen through translational repression, which stops proteins from being built. RNAi is a naturally occurring pathway found in many eukaryotes, which are organisms with complex cells. It serves as a vital defense system against parasitic nucleotide sequences like viruses or transposons. It also plays a major role in the development of living organisms.

The mechanism begins when double-stranded RNA (dsRNA) enters the cell's cytoplasm. This dsRNA can be exogenous, meaning it comes from outside the cell like a virus. It can also be endogenous, meaning it originates from within the cell's own genome. An enzyme called Dicer initiates the process by cleaving these long dsRNA molecules. Dicer acts like molecular scissors to produce short fragments called small interfering RNAs, or siRNAs. These siRNAs are typically 21 to 23 nucleotides in length.

Once the siRNAs are created, they must be loaded into a functional complex. A group called the RISC-Loading Complex, or RLC, helps manage this step. The RLC includes proteins like Dicer-2 and R2D2. A factor called TAF11 helps assemble this complex by increasing the binding affinity to siRNA by 10-fold. The siRNA is then unwound into two single strands: the passenger strand and the guide strand. The protein Argonaute 2 (Ago2) cleaves the passenger strand so it can be degraded. The guide strand is then incorporated into the RNA-induced silencing complex, known as RISC.

The RISC uses the guide strand to find and silence specific targets. The guide strand pairs with a complementary sequence on a target mRNA molecule. Once the match is found, Ago2 acts as a catalytic component to induce cleavage of the mRNA. This prevents the mRNA from acting as a template for protein translation. This specific type of destruction is called post-transcriptional silencing. In some organisms, this response can even spread systemically throughout the body.

There is another important type of molecule involved in this pathway called microRNA, or miRNA. While siRNAs usually come from outside the cell, miRNAs are encoded within the genome. They start as long primary transcripts called pri-miRNA in the nucleus. A microprocessor complex, including the enzyme Drosha, processes these into a 70-nucleotide stem-loop structure called pre-miRNA. This pre-miRNA is then exported to the cytoplasm to be processed by Dicer.

Unlike siRNAs, miRNAs often bind to the 3′ untranslated region (3′UTR) of an mRNA with imperfect complementarity. Instead of cutting the mRNA, they often block ribosomes from translating it into a protein.

Historically, scientists did not realize these processes were all the same. They used different names like co-suppression, quelling, or post-transcriptional gene silencing. The true identity of RNAi was revealed through the work of Andrew Fire and Craig Mello. They studied the nematode worm *Caenorhabditis elegans* and published their findings in 1998. Their discovery was so significant that they shared the 2006 Nobel Prize in Physiology or Medicine.

Today, RNAi is a powerful tool in both research and medicine. Scientists use synthetic dsRNA to perform large-scale screens to identify which genes are necessary for processes like cell division. It is also being developed for use in food, medicine, and even insecticides.

In humans, the regulation of miRNA is critical for health. As of 2023, the miRBase archive listed 28,645 miRNA entries across 271 species. Dysregulation of these pathways is linked to serious conditions. For example, changes in miRNA are associated with various cancers and neuropsychiatric disorders like Alzheimer's disease and autism.