Post-Transcriptional Modification
- In all kingdoms of life, gene expression can be regulated after an mRNA transcript has been produced
- Post-transcriptional modification of mRNA
- Helps prevent degradation
- mRNA is single stranded and therefore, inherently unstable
- Increases the efficiency of protein synthesis
- In eukaryotes, expands the complexity of the proteome
- Helps prevent degradation
- Prokaryotic mRNA does not require any significant post-transcriptional modification as translation can occur immediately which prevents degradation of the mRNA
- In eukaryotes, transcription and translation occur in separate parts of the cell, allowing for significant post-transcriptional modification to occur
- In eukaryotes, the immediate product of an mRNA transcript is called pre-mRNA which needs to be modified to form mature mRNA
- Three post-transcriptional events must occur
- A methylated cap is added to the 5' end to protect against degradation by exonucleases
- A poly-A tail (long chain of adenine nucleotides) is added to the 3' end for further protection and to help the transcript exit the nucleus
- Non-coding sequences (introns) are removed and coding sequences (exons) are joined together