RNA plays a multifaceted role in biology that is adaptable for many different applications in biotechnology. The most widely understood role of RNA is as messenger RNA. For many years, RNA was simply thought of as this intermediary with an important albeit limited function. It is now known that important gene regulation occurs at the level of RNA. Rather than simply controlling gene expression from the genome, organisms produce RNA that controls the mRNA translation into protein. In some organisms, antisense RNA is one way by which RNA controls protein translation. Antisense RNA binds to the complementary mRNA and blocks translation. From this discovery came the potential use of antisense RNA to block or attenuate synthesis of proteins that cause various diseases.
A second method of RNA-regulated gene expression is RNA interference (RNAi). Here small noncoding RNAs identify specific mRNAs and trigger their degradation. This fortuitous finding opened the door to a specific technique for controlling protein translation. Since RNA interference was discovered in 1993, its application has become widespread. The third novel role for RNA was the discovery that some RNA sequences can catalyze enzyme reactions themselves. Ribozymes, as they are called, are found in many different organisms, catalyzing cleavage and ligation of various substrates. This chapter focuses on the roles of antisense RNA, RNA interference, and ribozymes in biology and biotechnology.