Messenger RNA (mRNA) are the proteins are not synthesized directly from the genomic DNA. Insteadof that an RNA template (a precursor mRNA) is constructed from the sequence of gene. This RNA is then processed in number of ways, including splicing. Spliced single-stranded RNAs destined to become the templates for protein synthesis are called as mRNAs, The term mRNA is used only for the mature transcript with polyA tail and with all introns removed, rather than the primary transcript in nucleus. As such, an mRNA will have a 5' untranslated area, a coding area, a 3' untranslated area and (almost always) a poly(A) tail. Typically about 2% of total cellular RNA is mRNA.