Difference Between snRNA and snoRNA

Main Difference – snRNA vs snoRNA

snRNA and snoRNA are two types of small, non-coding RNA molecules found in the cell. Both snRNA and snoRNA are involved in modifying RNA just after the transcription. The snRNA is found in splicing speckles and Cajal bodies of the nucleus of the cell. The phosphorylated adaptor for nuclear export (PHAX) is involved in the transport of snRNA and snoRNA into the site of action in the nucleus. The main difference between snRNA and snoRNA is that snRNA is involved in the alternative splicing of pre-mRNA molecules to determine which sequence should be translated into a protein whereas snoRNA is involved in modifying rRNA and tRNA, mRNA editing, and genome imprinting.

Key Areas Covered

1. What is snRNA
      – Definition, Features, Function
2. What is snoRNA
      – Definition, Features, Function
3. What are the Similarities Between snRNA and snoRNA
      – Outline of Common Features
4. What is the Difference Between snRNA and snoRNA
      – Comparison of Key Differences

Key Terms: Alternative Splicing, Genome Imprinting, Modifying rRNA, mRNA Editing, Small nuclear RNA (snRNA), Small Nucleolar RNA (snoRNA), U-RNA

What is snRNA

Small nuclear RNA (snRNA) is a type of small non-coding RNA, comprising of 80 to 350 nucleotides in the molecules. The snRNA is also called U-RNA and they can be found in splicing speckles and Cajal bodies of the nucleus. The snRNA is a component of the small nuclear ribonucleoproteins (snRNPs), which forms the spliceosome controlling the splicing of pre-mRNA molecules during the post-transcriptional modifications. Eukaryotic pre-mRNA consists of both introns and exons. The introns should be removed from the sequence by splicing exons together.

Figure 1: RNA Splicing

The alternative splicing in eukaryotes produces different sequences of mRNA, forming several types of proteins. A spliceosome contains around 145 proteins. These proteins play a role in gene expression rather than splicing. The five types of snRNPs are involved in splicing are U1, U2, U4, U5, and U6. U2 and U6 begin the splicing. The removal of introns from pre-mRNA molecules is achieved based on three sequences. They are a 5’ splice site, a branch point, and a 3’ splice site. Typically, introns start with a GT and end with an AT. The alternative splicing is achieved by the complementary base pairing of a GT site with AT site of another intron. Around 15% single point mutations in the pre-mRNA may affect the process of splicing. The RNA splicing is shown in figure 1.

What is snoRNA

Small nucleolar RNA (snoRNA) is the other type of small non-coding RNA which is involved in the modification and processing of rRNA and tRNA precursors. The main function of the snoRNA is the maturation of rRNA during the formation of the ribosome. The snoRNA is involved in mRNA editing and genome imprinting as well. The snoRNA can be 80 to 1000 nucleotides in length in yeast.

Figure 2: Secondary structure of the C/D box snoRNA

Two types of snoRNA can be identified based on the distinct and evolutionarily conserved sequence elements present in each snoRNA. They are the C/D box and H/ACA box snoRNAs. The C/D box is involved in the 2′-O-methylation and the H/ACA box is involved in the pseudo-uridylation. Some of the snoRNAs are ubiquitous, some are tissue specific, and the others are imprinted. The secondary structure of the C/D box snoRNA is shown in figure 2.

Similarities Between snRNA and snoRNA

snRNA and snoRNA are types of small non-coding RNA in the cell.
Both snRNA and snoRNA are involved in modifying RNA inside the nucleus.
The phosphorylated adaptor for nuclear export (PHAX) is involved in the transport of each snRNA and snoRNA into the site of action in the nucleus.

Definition

snRNA: snRNA is a class of small RNA found in the nucleus of eukaryotes, involved in the pre-mRNA processing.

snoRNA: snoRNA is a type of small RNA, which guide the chemical modifications of rRNA and other RNAs like tRNA and snRNA.

Stands for

snRNA: snRNA stands for small nuclear RNA.

snoRNA: snoRNA stands for small nucleolar RNA.

Found in

snRNA: snRNA is only found in eukaryotes.

snoRNA: snoRNA can be found in both eukaryotes and archaea.

Size

snRNA: snRNA molecule is 80 to 350 nucleotides long.

snoRNA: snoRNA is 80 to 1000 nucleotides in length in yeast.

Function

snRNA: siRNA is involved in alternative splicing in eukaryotes.

snoRNA: snoRNA is involved in mRNA editing, modifying rRNA and tRNA, and genome imprinting.

Conclusion

snRNA and snoRNA are two types of small, non-coding RNA that are involved in the processing of precursor RNA. The snRNA is involved in the splicing of eukaryotic mRNA during post-transcriptional modifications. The snoRNA is involved in the maturation of rRNA and tRNA. Therefore, the main difference between snRNA and snoRNA is their function in the precursor RNA processing.

Reference:

1. “SnRNAs are required for splicing.” CELLS. N.p., n.d. Web. Available here. 24 July 2017.
2. “Eukaryotic snoRNAs: A paradigm for gene expression flexibility.” ScienceDirect. N.p., n.d. Web. Available here. 24 July 2017.
3. “MORE FUNCTIONAL RNA MOLECULES.” GENETICS. N.p., n.d. Web. Available here. 24 July 2017.

Image Courtesy:

1. “RNA splicing diagram en” By LadyofHats (Public Domain) via Commons Wikimedia
2. “RF00071” – taken from the Rfam database (Public Domain) via Commons Wikimedia