(mRNA) A linear single-stranded polynucleotide of uridine, adenine, guanidine, and cytidine monophosphates. mRNA is synthesized on DNA by mRNA polymerase enzyme, and the sequence of bases in it is a complementary copy (transcript) of the bases in one strand of DNA, the sense strand. The molecule initially manufactured on DNA now undergoes modification prior to its involvement in *protein synthesis
. This modification, called post-transcriptional processing, occurs in the nucleolus and involves the addition of adenine polynucleotide (poly A) to one end and a guanine derivative to the other end. In eukaryotic cells, post-transcriptional processing may also include excision of *introns
. Sometimes the term heterogeneous RNA (hnRNA) is given specifically to newly formed intron-containing mRNA, and the term mature mRNA is reserved for the molecule produced as a result of post-transcriptional processing. Mature mRNA moves to the ribosomes in the cytoplasm, where the triplets of bases in it act as a template and correspond to amino acids in proteins.