Brent Cornell

    
In eukaryotes, there are three post-transcriptional events that must occur in order to form mature messenger RNA:

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
• It also allows the transcript to be recognised by the cell’s translational machinery (e.g. 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 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
• Introns are intruding sequences whereas exons are expressing sequences
• The process by which introns are removed is called splicing

Post-Transcriptional Modifications

    
Splicing can also result in the removal of exons – a process known as alternative splicing

The selective removal of specific exons will result in the formation of different polypeptides from a single gene sequence

• For example, a particular protein may be membrane-bound or cytosolic depending on the presence of an anchoring motif

Alternative Splicing