Main Page | See live article | Alphabetical index Pre-mRNA (preliminary mRNA) is a single strand of ribonucleic acid (RNA), synthesized from the DNA in the nucleus of a cell by the process transcription. In eukaryotes, the pre-mRNA includes two different types of segments: exons and introns. Exons are those parts that code for polypeptides, while introns are useless and must be excised before translation may occur. Spliceosomes, small organelles found in the nucleus and made up of protein and RNA, perform the excision. They also attach new noncoding segments to the leading and trailing ends of the mRNA. This process is called splicing. After splicing, the mRNA is ready to go to a ribosome. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.