RNA sequencing is the process of determining the sequence of nucleotides in a strand of ribonucleic acid, or RNA. RNA is composed of four nucleotides called adenine (A), guanine (G), cytosine (S), and uracil (S). The particular sequence of the nucleotides is a "code" containing genetic information used to produce different types of proteins or to serve some specific function on its own. Genetic codes in the form of sequences of nucleotides define almost every biological process involving the development and function of an organism. RNA sequencing, then, is one type of research aimed at discovering the precise nature of that genetic code and at connecting the code to specific structures and functions within an organism.
Scientists sequence deoxyribonucleic acid, or DNA, far more often than they sequence RNA. DNA is similarly made up of nucleotides, but they are arranged in a double helix. RNA "transcripts" are actually made based on the sequence of nucleotides on a strand of DNA — DNA tends to be more robust than RNA because many RNA strands must be made from a single sequence of DNA. Additionally, DNA contains "introns," or noncoding segments of DNA, that are edited out during the transcription process and are, therefore, not detected by RNA sequencing. RNA sequencing is still important, though in many cases it is necessary to first "reverse-transcribe" RNA back to DNA before sequencing it.
The fact that an RNA sequence is not necessarily the same as the DNA sequence from which it was transcribed is one of the primary reasons that scientists actually conduct RNA sequencing experiments. RNA sequencing allows scientists to discover which parts of a DNA template were edited out during transcription. Knowing this, they can then examine how and why the sequence was edited out. One of the interesting problems in biology is the fact that a great deal of the genome, or summation of genetic information within an organism, seems to be unused. Learning exactly which sequences are used and which are not is an important step in exploring the intricacies of these unused segments of genetic information.
Developing more efficient and effective methods of RNA sequencing is an important focus of many researchers in biotechnology. Researchers must generally reverse-transcribe RNA to DNA before actually taking the sequence. Researchers want to develop methods that allow efficient direct sequencing of the RNA without damaging RNA strands. Additionally, researchers want to find high-throughput methods that allow them to sequence many RNA strands during one RNA sequencing process.