BOSTON (TheStreet) --RNA interference (RNAi for short) is a natural process of gene silencing in cells -- think of it as a genetic switch that when turned off, tells the body to stop making a certain protein.RNAi therapeutics are drugs that mimic this process. They potentially work by silencing specific messenger RNAs that are responsible for making disease-causing proteins. If you can prevent these proteins from being made, you can potentially stop or cure the disease. RNAi drugs are still in the early stages of clinical development, but the field is drawing a lot of attention from Big Pharma and smaller biotech startups, companies racing to develop the first successful RNAi-based drug. The 2006 Nobel Prize for Medicine was awarded to two RNAi research pioneers. Biotech investors, naturally, are also paying close attention to RNAi. To help in that effort, read on for more about seven drug and biotech companies focused on developing RNAi drugs.