What modifications occur to mRNA in eukaryotic cells after transcription?

Sourav PanNovember 9, 2024

Answered

After transcription, mRNA in eukaryotic cells undergoes several critical modifications to become mature and functional. These modifications include:

1. Capping

• 5′ Cap Addition: A 7-methylguanylate cap is added to the 5′ end of the mRNA shortly after transcription begins. This cap protects the mRNA from degradation by exonucleases and facilitates ribosome binding during translation initiation. The cap also plays a role in mRNA stability and nuclear export.

2. Polyadenylation

• 3′ Poly(A) Tail Addition: Following transcription, the 3′ end of the mRNA is cleaved and a tail of approximately 200-300 adenine nucleotides (poly(A) tail) is added. This modification enhances mRNA stability, aids in nuclear export, and is involved in the initiation of translation. The poly(A) tail also protects the mRNA from degradation in the cytoplasm.

3. Splicing

• Removal of Introns: Eukaryotic genes often contain non-coding sequences called introns that interrupt coding sequences (exons). During splicing, introns are removed, and exons are joined together to form a continuous coding sequence. This process is facilitated by a complex known as the spliceosome, which consists of small nuclear RNAs (snRNAs) and proteins. Splicing is essential for generating a functional mRNA that can be translated into protein.

4. Internal Modifications

• Chemical Modifications: In addition to capping, polyadenylation, and splicing, eukaryotic mRNAs can undergo various internal modifications, such as methylation (e.g., N^6-methyladenosine or m^6A), pseudouridine formation, and deamination. These modifications can influence mRNA stability, splicing efficiency, translation initiation, and overall gene expression regulation. For instance, m^6A modification has been shown to affect RNA metabolism by recruiting specific binding proteins that regulate mRNA fate