What are introns, and how do they affect the processing of genetic information?

Introns, a feature of eukaryotic DNA, are intervening stretches of DNA lying between the exons. The exons represent message material that actually gets translated into protein, whereas the introns must eventually be excised from the final mRNA product. Initially, both introns and exons are coded into an mRNA transcript. The existence of introns and exons was demonstrated when it was discovered that only about one-third of the primary transcript of DNA was used to make protein. In a highly complicated process, the intron regions are removed from the rough primary transcript on the DNA template to produce a secondary, mature mRNA that codes only for the exons. It is now clear that initiator and terminator signals must mark the beginning and end of each intron within a gene.
Despite the fact that the intron is not directly involved in shaping the final protein product, it appears to be essential to the synthesis of a functional mRNA. The process of excising the intron regions involves the participation of RNA as an enzyme. This catalytic RNA is part of a protein-RNA particle known as the small nuclear ribonucleoprotein particle.