RNA regulation Flashcards
What is the role of SR proteins in splicing?
Recruiting snRNPs to the spliceosome.
What happens to SR proteins after splicing?
They are dephosphorylated.
RNA exporter complex (REC)
Recruited by dephosphorylated SR proteins after splicing.
What does the RNA exporter complex (REC) associate with?
Transcription/export complex (TREX) at the 5′ end of mRNA.
Transcription/export complex (TREX)
Associates with REC at 5′ end of mRNA for export into cytoplasm.
What is the result of alternative splicing?
One gene encodes multiple mRNA transcripts to give many isoforms of protein.
What causes different splice patterns in alternative splicing?
Splicing complexes.
Cassette exons
Internal exons that are either retained or spliced out.
What happens to the first and last exons in alternative splicing?
They always remain in final splice forms.
What does an alternative splice site do?
<p>It is an alternative binding site for the spliceosome machinery.</p>
<p>-This means that part of an exon can be excluded or included. This can happen at the beginning or end of an exon, adjacent to an intron.</p>
Intron retention
<p>Introns are maintained in the transcript.</p>
<p>-This mechanism can occur in humans although is more commonly seen in lower eukaryotes such as plants and fungi.</p>
Where is intron retention more commonly seen?
In lower eukaryotes such as plants and fungi.
What can intron retention lead to?
<p>-The transcript with intronic regions can be degraded</p>
<p>-Nuclear retention and storage to await signal-induced splicing.</p>
How can intron retention change the open reading frame?
By identifying a different start codon for translation initiation.
Mutually exclusive exons
Either one or the other can appear in the final mRNA transcript but not both.
Alternative promoters
<p>Transcription factors bind to different regions within the promoter and recruit different splice complexes leading to a different first exon.</p>
What can alternative promoters lead to?
A different first exon.
Alternative polyadenylation
<p>The polyA site is found at the end of a different exon so the transcripts vary at the 3′ end. Therefore, the stop codon is in a different exon for each transcript.</p>
What is the location of the stop codon in alternative splicing transcripts?
It is in a different exon for each transcript.
Alternative Splicing
Mechanisms that generate different mRNA isoforms from a single gene.
What can alternative splicing be coupled to?
<p>Transcription.</p>
<p>-Different transcription factors can interact with different splice complexes.</p>
FLM transcription factor (plants)
Splice variants produced under different temperatures control flowering genes.
What ability do FLM splice variants have?
To either bind or not bind DNA.
Spliceoform
mRNA isoform produced by alternative splicing.
Splicing recap
Removal of introns • Joining of exons • Carried out be the spliceosome • Small nuclear ribonucleoprotein particles (snRNPs) carry out splicing • Splice factors/complexes containing SR proteins direct the spliceosome.
SR recap
Serine arginine (SR) proteins are responsible for recruiting snRNPs. • Phosphorylation of SR proteins allows them to move into the nucleus. • They associate with exon - splicing enhancer (ESE) sequences, DNA sequences within exons, to recruit the spliceosome.
What is the role of tissue-specific splice factors vs constitutive splicign
They ensure certain splice forms exist in specific tissues.
constitutive splicing is found in all cells and carries out fundemental splicing
example of cassete exons
with the troponin gene, which encodes a muscle fibre, that has 64 splice variants.
RNA editing significance
RNA editing, can lead to a change in the RNA sequence to modify a splice site, as seen in section on RNA editing.
Example of alternative promoters
One example of this use would be to change the localisation of a protein as localisation signals are often at the 5′ end.
