Question

RNases and proteases are enzymes that destroy RNAs and proteins, respectively. Which of the following enzymes when added to a spliceosome is predicted to prevent recognition of pre-mRNA regions critical for splicing? a. an RNase specific for tRNAs b. an RNase specific for snRNAs c. a protease specific for initiation factors d. a protease specific for a release factor

Short answer

The short answer is: (b) an RNase specific for snRNAs. This enzyme targets and destroys snRNAs, which are essential components of snRNPs in spliceosomes, thus preventing the proper recognition of pre-mRNA regions critical for the splicing process.

Step-by-step solution

Understanding Spliceosomes

Spliceosomes are large molecular complexes that remove introns from pre-messenger RNA (pre-mRNA) during the process of splicing. This process is essential for the proper expression of genes in eukaryotic cells. The spliceosome contains several small nuclear ribonucleoproteins (snRNPs) and additional proteins. SnRNAs are a key component of snRNPs and play a crucial role in splicing by recognizing sequences at the exon-intron boundaries.

Understanding the given enzyme options

We have four enzyme options to consider: a. An RNase specific for tRNAs: This enzyme would destroy tRNAs, which are responsible for bringing amino acids to ribosomes during translation. However, tRNAs are not involved in splicing. b. An RNase specific for snRNAs: This enzyme would destroy snRNAs, a component of snRNPs, which play an essential role in recognizing sequences necessary for splicing to occur. c. A protease specific for initiation factors: This enzyme would destroy initiation factors, which are essential in the translation process. However, these factors do not play a role in splicing. d. A protease specific for a release factor: This enzyme would destroy release factors, which are important for terminating translation. Again, these proteins are not involved in splicing.

Determining the correct enzyme

Based on our understanding of the spliceosome and the enzymes given, we can conclude that: - Enzymes targeting tRNAs, initiation factors, and release factors do not affect the splicing process, as they are involved in translation, not splicing. - The enzyme specifically targeting snRNAs, a component of snRNPs, is predicted to prevent recognition of pre-mRNA regions critical for splicing. By destroying snRNAs, the spliceosome would not function properly, thus preventing splicing.

Conclusion

The enzyme predicted to prevent recognition of pre-mRNA regions critical for splicing when added to a spliceosome is (b) an RNase specific for snRNAs.

Key concepts

snRNAs

Small nuclear RNAs, commonly known as snRNAs, play a crucial role in the function of the spliceosome. The spliceosome is a complex responsible for removing non-coding sequences called introns from pre-mRNA.
An important feature of snRNAs is their presence in small nuclear ribonucleoproteins, or snRNPs, which together form the core components of the spliceosome.

• snRNAs help in recognizing and binding to specific sequences at the exon-intron boundaries of pre-mRNA.
• They are vital for the splicing mechanism, guiding the assembly of the spliceosome and the precise cutting and joining of RNA segments.

Understanding the role of snRNAs
helps to appreciate why targeting them with an RNase would disrupt pre-mRNA splicing.

pre-mRNA splicing

Pre-mRNA splicing is an essential step in processing pre-mRNA to form mature mRNA. This process occurs within the nucleus of eukaryotic cells.
Splicing ensures that introns, or non-coding regions, are removed, leaving only coding sequences called exons to be expressed as proteins.

• The pre-mRNA is initially synthesized with both exons and introns.
• During splicing, the spliceosome orchestrates the removal of introns and the joining of exons.
• This process permits a single gene to encode multiple proteins through alternative splicing.

Pre-mRNA splicing not only allows for genetic diversity but also influences gene expression and cellular function.

RNA splicing enzymes

RNA splicing is facilitated by various enzymes and components within the spliceosome. These enzymes include RNA molecules and protein components that work together to execute precise RNA splicing. One of the pivotal categories of RNA splicing enzymes is RNases, which can degrade RNA molecules. Depending on their specificity, RNases can target different RNA types. For example:

• RNase specific for snRNAs can impair the function of the spliceosome, as snRNAs are crucial for recognizing splicing sites.
• Other RNases target distinct RNA molecules, like tRNAs, which do not affect splicing because tRNAs function in translation, not splicing.

Moreover, enzymes known as endonucleases and exosomes are involved in processing RNA molecules.
This helps to refine and modify RNA during and after splicing.
The specific action of these enzymes ensures the accurate removal of introns, allowing proper mRNA maturation.