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 is converted into a mature molecule that can then be translated into proteins. The post-transcriptional modification is not necessary for prokaryotic cells.

1. CHEMISTRY OF RNA
SPLICING
SUBMITTED BY:
EVELIN GEORGE,
19BCU006,
2ND B.Sc.BIOCHEMISTRY.

2. RNA SPLICING
 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.
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 is
converted into a mature molecule that can then be translated into proteins. The post-
transcriptional modification is not necessary for prokaryotic cells.
 RNA splicing is a controlled process that is regulated by various ribonucleoproteins.

3. 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.
 The word ‘introns’ is used to denote both the DNA sequences within the gene and the
corresponding sequence in RNA transcripts.
 Introns are common in the protein-coding nuclear genes of most jawed invertebrates other
eukaryotic organisms along with unicellular organisms like bacteria.
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.
 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 in prominent roles.
 Introns have a donor site (5′ end), a branch site (near the 3′ end), and an acceptor site (3′
end) that are required for splicing.

4. EXONS
 Exons are protein-coding DNA sequences that contain the necessary codons or genetic
information essential for protein synthesis.
 The word ‘exon’ represents the expressed region present in the genome.
 The exosome is the term used to indicate the entire set of all exons present in the
genome of the organisms.
 In genes coding for proteins, exons include both the protein-coding sequence and the 5’
 In genes coding for proteins, exons include both the protein-coding sequence and the 5’
and 3’ untranslated regions.
 Exons are found in all organisms ranging from jawed vertebrates to yeasts, bacteria, and
even viruses.
 Exons are essential units in protein synthesis as they carry regions composed of codons
that code for various proteins.
 Alternative splicing enables exons to be arranged in different combinations, where
different configuration results in different proteins.

6. STEPS IN SPLICING
There are two main steps in splicing:
 In the first step, the pre-mRNA is cut at the 5' splice site (the junction of the 5' exon and
the intron). The 5' end of the intron then is joined to the branch point within the intron.
This generates the lariat-shaped molecule characteristic of the splicing process
 In the second step, the 3' splice site is cut, and the two exons are joined together, and the
intron is released.
Many pre-mRNAs have a large number of exons that can be spliced together in different
 Many pre-mRNAs have a large number of exons that can be spliced together in different
combinations to generate different mature mRNAs. This is called alternative splicing, and
allows the production of many different proteins using relatively few genes, since a single
RNA can, by combining different exons during splicing, create many different protein
coding messages.
 Because of alternative splicing, each gene in our DNA gives rise, on average, to three
different proteins. Once protein coding messages have been processed by capping,
splicing and addition of a poly A tail, they are transported out of the nucleus to be
translated in the cytoplasm.

8. RNA SPLICING ERRORS
 The splicing of nuclear pre-mRNAs is a fundamental process required for the expression
of most metazoan genes. However, errors in splicing might occur due to mutations that
result in various splicing-related diseases.
 Mostly in alternative splicing, an erroneous splicing result in biological products that are
not functional.
 Errors during splicing might occur due to mutations at the splice site, which causes loss
of exons or inclusion of an intron disrupting the function of the RNA sequence.
of exons or inclusion of an intron disrupting the function of the RNA sequence.
 Similarly, displacement of a splice site might also cause the formation of longer or
shorter exons, resulting in erroneous products.
 In living organisms like plants, stress-induced alternative splicing associated with
various metabolic pathways might bring changes in the normal functioning of the plant.
 The chances of erroneous splicing is more in eukaryotic cells with high levels of
alternative splicing containing splice sites that have evolved to offer a weak binding
potential for components of the spliceosome

9. APPLICATION
 There are various biological, medical applications associated with pre-mature
RNA splicing, some of which are:
 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.
RNA sequence.
 RNA splicing also helps in the regulation of gene and protein content in the cell.
 Splicing of RNA sequences assists the process of evolution of new and
improved proteins.
 Various aberrant splicing isoforms act as markers for cancer and as targets
for cancer therapy.
 Pre-mRNA splicing is a key to the pathology of cancers where it regulates the
three functional aspects of cancer: proliferation, metastasis, and apoptosis.