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processes involved in the formation of mature, fully functional RNA species from primary RNA transcripts. For eukaryotic mRNA this may involve the removal of INTRONS (RNA splicing) and the addition of a cap at the 5′-end (See CAPPING (1)) and of a Poly(A) tail (see POLYADENYLATION). Generally little modification is made to prokaryotic mRNA; rRNA and tRNA in PROKARYOTES and EUKARYOTES are both modified. Both are cut out of large primary transcripts. For tRNA some of the bases are modified chemically. These processes occurring after TRANSCRIPTION are also called POSTTRANSCRIPTIONAL MODIFICATIONS.