RNA Splicing: Definition, Steps, Types and Examples

RNA splicing is an essential step in gene expression. It involves the removal of non-coding sequences called introns and the joining of coding sequences known as exons. This process produces mature RNA which is used in the process of protein synthesis. As a part of RNA processing, splicing enhances the accuracy of gene expression and ensures that the required parts of the gene are translated into proteins.

This Story also Contains

1. What Is RNA Splicing?
2. Types Of RNA Splicing
3. RNA Splicing Process
4. Regulation Of RNA Splicing
5. Splicing Treatment Strategies
6. RNA Splicing: A Critical Process
7. MCQs on RNA Splicing

This process plays a major role in the molecular basis of inheritance. It produces multiple proteins through a single gene. This increases the variation in the proteins and allows organisms to adapt to the changing environment. RNA splicing is also useful in biotechnology and medicine, especially in gene therapy and to regulate gene expression.

What Is RNA Splicing?

RNA splicing is one of the basic processes involved in gene expression in eukaryotic cells, in which pre-mRNA is converted into mature mRNA. In simple terms, splicing removes introns (non-coding sequences) from the RNA and joins together the exons (coding sequences). It ensures that only those sequences containing coding information are present in the mRNA for translation.

This forms the central mechanism of the flow of genetic information from DNA to RNA and then to proteins, what is known as the central dogma of molecular biology. The genetic code must remain accurate during RNA splicing so that the correct amino acid sequence is formed.

Types Of RNA Splicing

RNA splicing occurs in different ways depending on the types of RNA and the organisms. This variation allows a single gene to produce multiple proteins. It ensures only the coding regions of RNA are present for protein synthesis. The different types of RNA splicing are:

Constitutive Splicing

Constitutive splicing is the most primitive form, wherein introns are removed and exons are joined together in the order they are present in the gene. This type of splicing occurs in all cells and ensures that the genetic code is expressed precisely in the mRNA.

Alternative Splicing

Alternative splicing allows the generation of multiple proteins from a single gene. It excludes specific exons to make different mRNA transcripts. Some major types of alternative splicing include:

• Exon Skipping: The selective skipping of some exons is called exon skipping, resulting in alternative mRNA isoforms.

• Intron Retention: During this process, some introns are kept in the final mRNA and alter the function of the proteins.

• Mutually Exclusive Exons: Only one of the exons in a series is included in the mRNA.

• Alternate 5' Splice Site: Multiple splice sites are available at the 5' end of an exon.

• Alternate 3' Splice Site: Multiple splice sites are available at the 3' end of an exon.

Alternative splicing provides various means of increasing protein diversity so that one gene regulates several physiological processes and cellular functions.

RNA Splicing Process

The process of RNA splicing is a complicated, yet well-orchestrated series of events. The spliceosome is the key component of splicing. It is a huge RNA-protein complex including small nuclear RNAs (snRNAs) and associated proteins, which, with the spliceosome to help in the removal of introns and joining of exons. The steps of RNA splicing are as follows:

• Recognition of Splice Sites:

The spliceosome recognises specific sequences at the boundaries between an intron and an exon.

• Lariat Formation And Exon Ligation:

The intron loops into a lariat structure and then gets excised, while exons get joined.

• Release Of The Intron Lariat:

Release of the intron lariat and its degradation efficiency ensures that only the mature mRNA will enter the process of translation to synthesize protein.

Regulation Of RNA Splicing

RNA splicing is regulated by both cis-acting elements and transacting factors. It ensures that the correct form of RNA is produced. It allows cells to make different proteins from the same gene through splicing. Proper regulation is important for normal development and functioning.

Cis-Acting Element

These are the splicing enhancers and silencers. They are either within the exons, known as the exonic splicing enhancers/silencers, or in the introns, called intronic splicing enhancers/ silencers. The effectiveness of this element is based on the splicing factors with which they bind.

Trans Acting Factors

Trans acting factors are special proteins that help regulate RNA splicing. They work by interacting with spliceosomes. These factors respond to the signals from the cell and its environment. This enables the cells to adapt to a spectrum of physiological conditions and stressors.

RNA Splicing Errors And Diseases

It forms the basis for several human genetic disorders, as RNA splicing errors can be lethal. Mutations at splice sites or regulatory elements disturb normal splicing patterns and lead to abnormal mRNA and hence, dysfunctional protein.

For example:

Spinal Muscular Atrophy: Caused by mutations in the SMN1 gene that affect the splicing of the SMN2 pre-mRNA.

Cystic Fibrosis: Splicing mistakes in the CFTR gene lead to aberrant splicing and reduce the chloride ion transport.

Splicing Treatment Strategies

New and effective treatments are being developed to correct splicing mistakes. In gene therapy, functional copies of the defective genes are added. Another method uses special molecules called splice-switching oligonucleotides that change the splicing patterns. These can help treat splicing-related diseases.

RNA Splicing: A Critical Process

RNA splicing is carried out to generate the huge diversity of proteins required for various functions within a living organism. This process allows cells to express different isoforms of proteins from one gene, therefore increasing genome diversity. Moreover, splicing regulation allows tissue-specific expression and adaptation to environmental changes. Hence, it is crucial for development, cell differentiation, and cellular stress response.

Conclusion

RNA splicing is a universal, complex process, and its proper execution is required for appropriate gene regulation and expression. Constitutive and alternative splicing mechanisms allow cells to generate diverse proteins from a relatively few number of genes. The regulation of RNA splicing ensures the correct expression of the genetic information. Error in splicing can cause serious diseases. Understanding RNA splicing helps scientists find new treatments and understand gene expression and regulation.

MCQs on RNA Splicing

Q1. Which process eliminates the introns in eukaryotic transcription?

1. Splicing

2. Poly-A- tail

3. Alternative editing

4. Capping

Correct answer: 1) Splicing

Explanation:

Splicing is important during the process of eukaryotic transcription when introns are removed from the pre-mRNA sequence. Such elimination is required for producing mature mRNA that includes only coding regions referred to as exons. This modification helps in the proper processing of mRNA before translation so that correct proteins can be synthesized. Such a modification is very critical in gene expression and adds diversity to the products made by the eukaryotic cells.

Hence, the correct answer is Option 1) Splicing.

Q2. About mature mRNA in eukaryotes:

1. Exons and introns do not appear in the mature RNA.

2. Exons appear but introns do not appear in the mature RNA.

3. Introns appear but exons do not appear in the mature RNA.

4. Both exons and introns appear in the mature RNA.

Correct answer: 2) Exons appear but introns do not appear in the mature RNA

Explanation:

• The coding sections of the gene that contain the instructions needed to synthesize proteins are called exons.

• RNA splicing eliminates introns which are non-coding areas that are located in between exons.

• RNA splicing creates the final mature mRNA by joining the exons and removing the introns. The translation process uses this mature mRNA to create proteins.

• Accordingly, only the exons and not the introns are found in the mature mRNA that leaves the nucleus.

Hence, the correct answer is option 2) Exons appear but introns do not appear in the mature RNA.

Also Read:

• MCQs on Transcription in Eukaryotes and RNA Processing

• Bacterial Genetics

• Salient Features of Double Helix Structure of DNA