<P> Post-transcriptional modification or Co-transcriptional modification is the process in eukaryotic cells where primary transcript RNA is converted into mature RNA . A notable example is the conversion of precursor messenger RNA into mature messenger RNA (mRNA) that occurs prior to protein translation . The process includes three major steps: addition of a 5' cap, addition of a 3' poly - adenylation tail, and splicing . This process is vital for the correct translation of the genomes of eukaryotes because the initial precursor mRNA produced during transcription contains both exons (coding or important sequences involved in translation), and introns (non-coding sequences). </P> <Table> <Tr> <Td> <Table> <Tr> <Td> Regulatory sequence Regulatory sequence Enhancer / silencer Promoter 5'UTR Open reading frame 3'UTR Enhancer / silencer Proximal Core Start Stop Terminator Transcription DNA Exon Exon Exon Intron Intron Post-transcriptional modification Pre - mRNA Protein coding region 5'cap Poly - A tail Translation Mature mRNA Protein The structure of a eukaryotic protein - coding gene . Regulatory sequence controls when and where expression occurs for the protein coding region (red). Promoter and enhancer regions (yellow) regulate the transcription of the gene into a pre-mRNA which is modified to remove introns (light grey) and add a 5' cap and poly - A tail (dark grey). The mRNA 5' and 3' untranslated regions (blue) regulate translation into the final protein product . </Td> </Tr> </Table> <Table> <Tr> <Td> Polycistronic operon Regulatory sequence Regulatory sequence Enhancer Enhancer / silencer / silencer Operator Promoter 5'UTR ORF ORF UTR 3'UTR Start Start Stop Stop Terminator Transcription DNA RBS RBS Protein coding region Protein coding region mRNA Translation Protein The structure of a prokaryotic operon of protein - coding genes . Regulatory sequence controls when expression occurs for the multiple protein coding regions (red). Promoter, operator and enhancer regions (yellow) regulate the transcription of the gene into an mRNA . The mRNA untranslated regions (blue) regulate translation into the final protein products . </Td> </Tr> </Table> </Td> </Tr> </Table>

How rna is edited prior to leaving the nucleus