Because the work of joining the strand of nucleotide is always done by ligase enzyme.... Wether it is DNA or RNA... however in both the cases the specificity of enzyme will be different respecivelly but their class will be LIGASE only...

Splicing and the enzyme involved

Splicing is a crucial process that occurs in eukaryotic cells during gene expression. It involves the removal of introns (non-coding regions) from the pre-mRNA and joining of exons (coding regions) to form a mature mRNA molecule that can be translated into a protein. The enzyme responsible for catalyzing this reaction is known as RNA ligase.

RNA Ligase

RNA ligase is an enzyme that plays a key role in the splicing process. It is responsible for joining the ends of the exons together after the introns have been removed. RNA ligase catalyzes a reaction known as ligation, which involves the formation of a phosphodiester bond between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of another nucleotide.

Mechanism of splicing

The process of splicing involves several steps and is carried out by a large complex of proteins and small nuclear ribonucleoproteins (snRNPs) called the spliceosome. The spliceosome recognizes specific sequences at the boundaries between exons and introns and brings them together for splicing.

1. Recognition of intron/exon boundaries: The spliceosome identifies the 5' splice site (GU) at the beginning of the intron and the 3' splice site (AG) at the end of the intron. These sequences are recognized by snRNPs called U1 and U2, respectively.

2. Formation of the spliceosome: Additional snRNPs, along with other proteins, assemble to form the spliceosome. This complex positions the exons and introns in the correct orientation for splicing.

3. Cleavage at the 5' splice site: The spliceosome cleaves the phosphodiester bond at the 5' splice site, releasing the intron as a lariat structure.

4. Joining of exons: The 3' hydroxyl group at the end of the upstream exon attacks the 5' phosphate group at the beginning of the downstream exon, forming a phosphodiester bond. This reaction is catalyzed by RNA ligase.

5. Release of spliced mRNA: After the splicing reaction is complete, the intron is released as a lariat structure, and the mature mRNA molecule containing only exons is ready for translation.

Conclusion

In summary, during the splicing process, exons are joined together by the enzyme RNA ligase. RNA ligase catalyzes the formation of phosphodiester bonds between the ends of exons, resulting in the removal of introns and the formation of a mature mRNA molecule. This process is essential for the proper expression of genes in eukaryotic cells.