RNA splicing is a biological process where a newly synthesized pre-mRNA transcript is processed and transformed into mRNA. It involves the removing of non-coding regions of RNA (introns) and the joining of the coding regions (exons).

1. A PRESENTATION ON -
RNA SPLICING
SHRI SHANKARACHARYA MAHAVIDYALAYA
GUIDED BY-
Dr. Rachana Choudhary Mam
(HEAD OF DEPT. ,MICROBIOLOGY)
SUBMITTED BY-
Anisha Kazi
M.Sc Semester II
(Microbiology)

2. SYNOPSIS:
❖ INTRODUCTION
❖ HISTORY
❖ DEFINITION
❖ WHAT ARE INTRONS?
❖ WHAT ARE EXONS?
❖ WHAT ARE SPLICEOSOMES?
❖ MECHANISM OF RNA SPLICING
❖ TYPES OF RNA SPLICING
❖ APPLICATIONS
❖ CONCLUSION
❖ REFERENCES

3. INTRODUCTION:
RNA splicing is a form of RNA processing in which a newly made precursor messenger
RNA(mRNA) is transformed into a mature RNA by removing the non-coding sequences termed
INTRONS.
The process of RNA splicing involves the removal of non-coding sequences or introns and
joining of the coding sequences or exons.
RNA splicing takes place during or immediately after transcription within the nucleus in the
case of nucleus-encoded genes.
In eukaryotic cells, RNA splicing is crucial as it ensures that an immature RNA molecule can be
translated into proteins
The post-transcriptional modifications is not necessary for prokaryotic cells
RNA splicing is a controlled process that is regulated by various ribonucleoproteins.
-

4. HISTORY:
RNA Splicing was discovered by
two scientists Phillip Allen Sharp
and Richard J.Roberts .
They were awarded the Nobel
Prize in Physiology & Medicine for
their achievement in the year 1993.
Phillip Allen Sharp Richard J.Roberts

5. definition:
“RNA splicing is a biological process where a newly synthesized pre-mRNA transcript is
processed and transformed into mRNA. It involves the removing of non-coding regions of RNA
(introns) and the joining of the coding regions (exons).”
whAT ARE INTRONS ?
Introns are non-coding DNA sequences present within a gene that are removed by the
process of RNA splicing during maturation of the RNA transcript.
They are common in protein coding nuclear-genes of mostly jawed invertebrates,other
eukaryotic organisms along with unicellular organisms like bacteria.
Similarly, the mitochondrial genomes of jawed vertebrates are almost entirely devoid of
introns whereas those in other eukaryotes have many introns.

6. During RNA splicing, the introns between the exons are removed to connect two
different exons that then code for messenger RNA.
INTRONS are crucial because the variation in the protein bio-product formed is
greatly enhanced by alternative splicing in which introns take part prominent
roles.
FIG: DEPICTING INTRON AND ITS SPLICING

7. WHAT ARE EXONS?
Exons are protein coding DNA sequences that
contains the necessary codons or genetic
information essential for protein synthesis.
In genes,coding for proteins,exons include both
the protein-coding sequences and the 5’ & 3’
untranslated regions.
Exons are found in all organisms ranging from
jawed vertebrates to yeasts , bacteria & even
viruses.in the human genome , exons account
only for 1% of the total genome while the rest is
occupied by intergenic DNA and introns.
Exons are essential unit in protein synthesis as
they carry regions composed of codons that
code for various proteins.
fig: depicting exons and its mechanisms

8. WHAT ARE SPLICEOSOME?
A spliceosome is a large and complex molecule formed
of RNAs and proteins that regulate the process of RNA
splicing.
The spliceosomes is composed of five small nuclear
RNAs (snRNA) and about 80 protein molecules. The
combination of RNAs with these proteins results in the
formation of an RNA-protein complex termed as small-
nuclear ribonucleoproteins(snRNPs).
The spliceosomes functions as an editor that selectively
cuts out unnecessary and incorrect materials (introns)
to produce a final cut.
All spliceosomes are involved in both the removal of
introns and the ligation of remaining exons.
Fig :Image depicting spliceosomes

9. Mechanism of rna splicing:
➢ The process of RNA splicing begins with the binding of the ribonucleoproteins
or spliceosomes to the introns present on the splice site.
➢ The binding of the spliceosome results in a biochemical process called
transesterification between RNA nucleotides.
➢ During this reaction, the 3’OH group of a specific nucleotide on the intron, which
is defined during spliceosome assembly, causes a nucleophilic attack on the first
nucleotide of the intron at the 5’ splice site.
➢ This causes the folding of the 5’ and 3’ ends, resulting in a loop. Meanwhile, the
adjacent exons are also brought together.
➢ Finally, the looped intron is detached from the sequence by the spliceosomes.

10. Mechanism of rna splicing:
➢ Now, a second transesterification reaction occurs during the ligation of adjacent
exon segments.
➢ In this case, the 3’OH group of the released 5’ exon then performs an electrophilic
attack on the first nucleotide present just behind the last nucleotide of the intron at
the 3’ splice site.
➢ This causes the binding of the two exon segments along with the removal of the
intron segment.
➢ Earlier, the intron released during splicing is thought of as a junk unit. Still, it has
been recently observed that these introns are involved in other processes related to
proteins after their removal.
➢ Besides the spliceosomes, another group of protein/ enzymes termed ‘ribozymes’ are
also involved in the control and regulation of the splicing process.

11. FIG: MECHANISM OF RNA SPLICING

12. TYPES OF RNA SPLICING:
SELF-SPLICING
ALTERNATIVE
SPLICING
RNA
SPLICING
t-RNA
SPLICING

13. SELF-SPLICING:
Self-splicing is a type of RNA splicing which occurs in
some rare introns that are capable of promoting
phosphodiester bond cleavage and formation without the
help of other proteins or spliceosomes.
There are three types of self-splicing introns that are
grouped as Group I, Group II, and Group III.
Group I and Group II introns perform the splicing process in
a mechanism similar to that by spliceosomes. These
suggest that these introns might be evolutionarily related
to the spliceosomes.
The introns can catalyse their own excision from their
parent RNA. Some of the genes undergo self-splicing, e.g.
phage genes, protozoan ribosomal RNA genes, etc. Some
mitochondrial genes are also capable of self-splicing.
FIG: SELF SPLICING OF RNA

14. ALTERNATE
SPLICING:
Alternative splicing is a splicing process resulting in a varying composition of exons in the same RNA and creating a range of
unique proteins.
Alternative splicing of pre-mRNA is an essential mechanism to enhance the complexity of gene expression, and it also plays a
vital role in cellular differentiation and organism development.
The process of alternative splicing might occur either by skipping or extending some exons or by retaining particular introns,
resulting in different varieties of mRNA formed.
Regulation of alternative splicing is a complex process in which numerous components interact with each other, including cis-
acting elements and trans-acting factors.
The process is further guided by the functional coupling between transcription and splicing.
Additional molecular features, such as chromatin structure, RNA structure, and alternative transcription initiation or alternative
transcription termination, collaborate with these basic components to generate the protein diversity due to alternative splicing.
Alternative splicing is also essential for other functions like the identification of novel diagnostic and prognostic biomarkers, as
well as new strategies for therapy in cancer patients.
Thus, alternative splicing has a role in almost every aspect of protein function, including binding between proteins and ligands,
nucleic acids or membranes, localization, and enzymatic properties.

15. FIG: ALTERNATE SPLICING OF RNA

16. T-RNA SPLICING:
● Like in mRNA, the genes in tRNA are also interrupted by introns, but here the splicing mechanism is quite
different.
● Splicing in tRNA is catalyzed by three enzymes with an intrinsic requirement for ATP hydrolysis.
● The process of tRNA splicing occurs in all three major lines of descent, the Bacteria, the Archaea, and the
Eukarya, but the mechanism might differ in bacteria and higher organisms.
● In bacteria, the introns in the tRNA are self-splicing.
● In Archaea and Eukarya, however, the tRNA splicing reaction occurs in three steps where each step is
catalyzed by a distinct enzyme, each of which can function interchangeably on all of the substrates.
● In the first step, the pre-tRNA is cleaved at the two splice sites by an endonuclease, resulting in two tRNA
half molecules and a linear intron with 5’-OH and 3’-cyclic PO4 ends.
● The cleavage is then followed by the ligation of the two RNA half molecules in the presence of a tRNA ligase
enzyme.
● Finally, the PO4 ends produced from splicing are transferred to NAD in a process catalyzed by nicotinamide
adenine dinucleotide (NAD)-dependent phosphotransferase.

17. APPLICATIONS OF RNA SPLICING:
There are various biological, medical applications associated with pre-mature RNA splicing, some of
which are:
1. Pre-mRNA splicing is a fundamental process in cellular metabolism that plays an essential role
in generating protein diversity. The diversity is brought about by changes in the number and
sequence of exons and introns present in the RNA sequence.
2. RNA splicing also helps in the regulation of gene and protein content in the cell.
3. Splicing of RNA sequences assists the process of evolution of new and improved proteins.
4. Various aberrant splicing isoforms act as markers for cancer and as targets for cancer
therapy.
5. Pre-mRNA splicing is a key to the pathology of cancers where it regulates the three functional
aspects of cancer: proliferation, metastasis, and apoptosis.

18. CONCLUSION:
RNA splicing is the process by which the newly synthesized pre-mRNA, also known as hnRNA, (heterogeneous
nuclear RNA) is processed and forms the mature mRNA. hnRNA is processed in the nucleus and converted to
mRNA, which then comes to the cytoplasm and undergoes translation or protein synthesis. It is a post-
transcriptional modification.
RNA splicing facilitates the formation of multiple functional mRNAs from a single transcript, which codes for
different proteins.
It also helps in the regulation of gene expression and protein content of the cell.
It assists in the evolution process by forming different combinations of exons and thereby making new and
improved proteins.
New exons can be inserted into the introns to create new proteins without disrupting the functionality of the
original gene.

19. REFERENCES:
TEXTBOOK FROM-
❏ Genetics by B.D Singh.
❏ Molecular & Cell Biology by H Lodish et al.
❏ Essential Cell Biology by Alberts et al.
❏ Cell & Molecular Biology by G.Karp
❏ Cell Biology by C.B Pawar.