A computer-generated representation of RNA.
Researchers have successfully used a technique that selectively shuts off genes to lower levels of LDL, or "bad" cholesterol, in mice. The findings, reported in the journal Nature, suggest that RNA interference may be a revolutionary development for medical science. NPR's Joe Palca reports.
RNA Interference: An Explainer
Genes are made up of chunks of DNA. Each gene contains the instructions to make a particular protein. Proteins do the work of our cells -- digesting food, releasing energy, sending signals to other cells.
To make a protein, another molecule called RNA (ribonucleic acid) reads the DNA instructions and then directs the protein's assembly. Think of RNA as a construction worker, who actually builds a house after reading an architect's drawings.
Most RNA is single stranded. Until 1998, researchers had thought only single-stranded RNA had an effect on gene expression. But recently, scientists discovered that relatively short, double-stranded RNA can be used to turn off certain genes -- without triggering a defensive response that results in cell suicide. This selective silencing of specific genes is called RNA interference, or RNAi.
In the Nov. 11, 2004, issue of Nature, scientists report they were able to use RNAi to lower cholesterol in mice. The researchers, affiliated with Massachusetts-based Alnylam Pharmaceuticals, used RNAi to turn off ApoB, the gene responsible for making the "bad" cholesterol known as LDL.
1. Scientists create a short, double-stranded RNA with a genetic code complementary to that of the targeted disease-causing gene — in this case, the "bad" cholesterol-causing ApoB.
2. Within a cell, this short, double-stranded RNA unwinds and gets incorporated into an RNA-protein complex — in this case, a compound that resembles cholesterol. Cells that make cholesterol also take up cholesterol, so adding the cholesterol molecule to the RNA ensures that the complex is taken up by the targeted cells.
3. Inside cells, the two strands of the targeted RNA unwind and degrade. This shuts off the production of the targeted protein — ApoB.