Exons are regions of DNA that are transcribed to RNA and retained after introns are spliced out. They are coding sections of an RNA transcript, or the DNA encoding it, that are translated into protein. Exons can be separated by intervening sections of DNA that do not code for proteins, known as introns. Following transcription, new, immature strands of messenger RNA, called pre-mRNA, may contain both introns and exons. These pre-mRNA molecules go through a modification process in the nucleus called splicing during which the noncoding introns are cut out and only the coding exons remain. Splicing produces a mature messenger RNA molecule that is then translated into a protein.
It is important to note that not all exons are protein-coding, and the term "exon" is often misused to refer only to protein-coding exons. Some exons are non-coding, meaning they do not contain information for making a protein.
