Small nuclear RNA

Small nuclear RNA (snRNA) is a class of small RNA molecules that are found within the nucleus of eukaryotic cells. These molecules play a critical role in the splicing of pre-mRNA into messenger RNA (mRNA), a process essential for the translation of genetic information from DNA to proteins. snRNAs are components of a complex known as spliceosome, which is responsible for the removal of introns from pre-mRNA.

Function

The primary function of snRNA is to participate in the RNA splicing process. snRNAs form complexes with proteins, creating small nuclear ribonucleoproteins (snRNPs). These snRNPs are essential components of the spliceosome. The spliceosome recognizes the splice sites on the pre-mRNA and catalyzes the removal of introns, joining the exons together to form a continuous coding sequence. This process is crucial for the generation of functional mRNA that can be translated into proteins.

Types of snRNA

There are several types of snRNA, each with a specific role in the splicing process. The most well-known snRNAs are U1, U2, U4, U5, and U6. Each of these snRNAs recognizes specific nucleotide sequences on the pre-mRNA and contributes to the assembly and function of the spliceosome.

• U1 snRNA: Binds to the 5' splice site of the pre-mRNA.
• U2 snRNA: Binds to the branch point sequence, playing a key role in the formation of the lariat structure during splicing.
• U4 snRNA: Interacts with U6 snRNA and is involved in the assembly of the spliceosome.
• U5 snRNA: Binds to exons at the splice junctions, ensuring accurate splicing.
• U6 snRNA: Interacts with U2 snRNA and is crucial for the catalytic activity of the spliceosome.

Biogenesis

The biogenesis of snRNA involves transcription by either RNA polymerase II or RNA polymerase III, depending on the type of snRNA. After transcription, snRNAs undergo several processing steps, including 5' cap addition, 3' end trimming, and the addition of a Sm protein complex to the Sm site. These modifications are essential for the stability, localization, and function of snRNAs within the nucleus.

Clinical Significance

Alterations in snRNA and the splicing process can lead to various diseases, including cancer, spinal muscular atrophy, and retinitis pigmentosa. Understanding the mechanisms of snRNA function and splicing can provide insights into the pathogenesis of these diseases and offer potential targets for therapeutic intervention.

See Also

• RNA splicing
• Spliceosome
• Messenger RNA (mRNA)
• Eukaryotic transcription