In eukaryotes, there are three post-transcriptional events that must occur in order to form messenger RNA (mRNA)

• Prokaryotic cells do not undertake these events due to their lack of compartmentalisation and more compact genomes
  

Capping

• Capping involves the addition of a methyl group to the 5’-end of the transcribed RNA
  

• The methylated cap provides protection against degradation by exonucleases and also allows the transcript to be recognised by the cell’s translational machinery (nuclear export proteins and ribosome)
  

Polyadenylation

• Polyadenylation describes the addition of a long chain of adenine nucleotides (a poly-A tail) to the 3’-end of the transcript
  

• The poly-A tail improves the stability of the RNA transcript and facilitates its export from the nucleus
  

Splicing

• Within eukaryotic genes are non-coding sequences called introns, which must be removed (via splicing) prior to forming mature mRNA
  

• The coding regions are called exons and these are fused together when introns are removed to form a continuous sequence
  

  • In other words, introns are intruding sequences whereas exons are expressing sequences

RNA Processing