Splicing of Transcription Unit

Splicing is the process of removing introns and joining the exons in a defined order in a transcription unit. The process of splicing is essential for generating mature mRNA molecules that can be translated into proteins.

Steps of Splicing

1. Recognition of intron/exon boundaries: The splicing process is initiated by the recognition of specific sequences at the 5' and 3' ends of the intron.

2. Formation of spliceosome: The spliceosome is a complex of small nuclear ribonucleoproteins (snRNPs) and other proteins that assemble at the intron/exon boundaries to catalyze the splicing reaction.

3. Cleavage of 5' intron boundary: The spliceosome cleaves the 5' end of the intron and forms a lariat structure with the 5' end of the intron covalently bound to a specific adenosine residue within the intron.

4. Cleavage of 3' intron boundary: The spliceosome cleaves the 3' end of the intron, and the free 3' end of the exon is ligated to the 5' end of the following exon.

5. Release of lariat structure: The lariat structure is then released, and the spliced mRNA molecule is formed.

Importance of Splicing

Splicing is a crucial step in gene expression as it allows for the generation of multiple protein isoforms from a single gene. It also plays a critical role in regulating gene expression by allowing for the inclusion or exclusion of specific exons, which can affect the function of the resulting protein. Any errors in the splicing process can lead to genetic disorders, including cancers and inherited diseases.

Eukaryotic genes that contain introns, splicing is usually required in order to create an mRNA molecule that can be translated into protein. For many eukaryotic introns, splicing is carried out in a series of reactions which are catalyzed by the spliceosome, a complex of small nuclear ribonucleo proteins (snRNPs). Self-splicing introns, or ribozymes capable of catalyzing their own excision from their parent RNA molecule, also exist.