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In
molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
, an exonic splicing enhancer (ESE) is a DNA
sequence motif In biology, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and usually assumed to be related to biological function of the macromolecule. For example, an ''N''-glycosylation site motif can be defined as '' ...
consisting of 6 bases within an
exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequenc ...
that directs, or enhances, accurate splicing of heterogeneous nuclear RNA ( hnRNA) or
pre-mRNA A primary transcript is the single-stranded ribonucleic acid (RNA) product synthesized by transcription of DNA, and processed to yield various mature RNA products such as mRNAs, tRNAs, and rRNAs. The primary transcripts designated to be mRNAs ...
into messenger RNA (
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...
).


Introduction

Short sequences of DNA are transcribed to
RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
; then this RNA is translated to a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
. A gene located in DNA will contain
introns An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene ...
and
exons An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequenc ...
. Part of the process of preparing the RNA includes splicing out the introns, sections of RNA that do not code for the protein. The presence of exonic splicing enhancers is essential for proper identification of splice sites by the cellular machinery.


Role in splicing

SR proteins bind to and promote exon splicing in regions with ESEs, while
heterogeneous ribonucleoprotein particle Heterogeneous nuclear ribonucleoproteins (hnRNPs) are complexes of RNA and protein present in the cell nucleus during gene transcription and subsequent post-transcriptional modification of the newly synthesized RNA (pre-mRNA). The presence of the pr ...
s (hnRNPs) bind to and block exon splicing in regions with exonic splicing silencers. Both types of proteins are involved in the assembly and proper functioning of
spliceosome A spliceosome is a large ribonucleoprotein (RNP) complex found primarily within the nucleus of eukaryotic cells. The spliceosome is assembled from small nuclear RNAs ( snRNA) and numerous proteins. Small nuclear RNA (snRNA) molecules bind to sp ...
s. During
RNA splicing RNA splicing is a process in molecular biology where a newly-made precursor messenger RNA (pre-mRNA) transcript is transformed into a mature messenger RNA (mRNA). It works by removing all the introns (non-coding regions of RNA) and ''splicing'' b ...
,
U2 small nuclear RNA auxiliary factor 1 Splicing factor U2AF 35 kDa subunit is a protein that in humans is encoded by the ''U2AF1'' gene. Function This gene belongs to the splicing factor SR family of genes . U2AF1 is a subunit of the U2 Auxiliary Factor complex alongside a larger ...
(U2AF35) and
U2AF2 Splicing factor U2AF 65 kDa subunit is a protein that in humans is encoded by the ''U2AF2'' gene. Function In eukaryotes, the introns in the transcribed pre-mRNA first have to be removed by spliceosome in order to form a mature mRNA. A spliceo ...
(U2AF65) interact with the branch site and the 3' splice site of the intron to form the lariat. It is thought that SR proteins that bind to ESEs promote exon splicing by increasing interactions with U2AF35 and U2AF65. Mutation of exonic splicing enhancer motifs is a significant contributor to genetic disorders and some cancers. Simple point mutations in ESEs can inhibit affinity for splicing factors and alter alternative splicing, leading to altered mRNA sequence and protein translation. A field of genetic research is dedicated to determining the location and significance of ESE motifs
in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
.


Research

Computational methods were used to identify 238 candidate ESEs. ESEs are clinically significant because synonymous point mutations previously thought to be silent mutations located in an ESEs can lead to exon skipping and the production of a non functioning protein. Disruption of an exon splicing enhancer in exon 3 of
MLH1 DNA mismatch repair protein Mlh1 or MutL protein homolog 1 is a protein that in humans is encoded by the MLH1 gene located on chromosome 3. It is a gene commonly associated with hereditary nonpolyposis colorectal cancer. Orthologs of human MLH1 ...
gene is the cause of HNPCC (hereditary nonpolyposis colorectal cancer) in a Quebec family. There is evidence that these 236 hexamers that signal splicing are evolutionarily conserved.


See also

* Exonic splicing silencer (ESS)


References

{{reflist


External links


ESE finder
Genetics