RNA Splicing Flashcards
how many types of introns are there?
4; Group I and II, pre-mRNA, and tRNA, all removed in unique ways
how does splicing of pre-mRNA introns occur?
uses a protein-RNA complex similar to ribosomes & signal recognition particles for cellular protein trafficking; –> use snRNPs;;
3 important regions–>5’ splice site (GU); 3’ splice site (AG), branch site (middleish, A)
splicing rxn of snurps
the G of the GU at 5’ site is released and attaches to the A of the branch site; the last base of the first exon attaches the to the first base ofn the next exon; intron lariat is released and degraded–catalyzed by the spliceosome
describe the spliceosome rxn pathway
- U1 binds the 5’ splice site; 2. U2 binds th branch site to make the A accessible; 3. U5 and U4/6 binds to U1; 4. U4 releases U6 so it can bind the splice site; 5. U1 is removed from the splice site; 6. U6 and U2 come together and bring 5’ splice site to the branch site–>forms lariat 7. U5 takes the 5’ exon (now liberated) to the 3’ splice site and the intron is released
how do group II introns splice out?
use the same 5’, 3’ and branch site seqs as pre-mRNA but do not require a protein
how do group I introns splice out?
use free guanosine as the branch site instead of internal adenine–> do not form a lariat; also do not require a protein
what is the “introns early” theory of intron origin?
introns present before proks and euks split; self-splicing introns were used to shuffle protein subunits around–could not only splice out but in as well; after a period of shuffling many genes with diverse proteins were formed; most proks have lost their introns to relieve metabolic load (energy to make the DNA, RNA, then splice out);
what is the introns late theory?
late = prok/euk split–>still early in euk evoluton; a seq existed with self-splicing capabilities–>within this intron was a reverse transcriptase ORF which arose/inserted and the RNA was reverse transcribed into various genes; these type II introns did not require other factors to be spliced; as proteins were selected for to make the process more efficient (our spliceosome) introns could mutate and form nonsplicing introns; once introns could take on “any” seq, they could become regualtory
what is a piece of evidence for mobile introns?
twintrons–one intron spliced into another
What is the role of ISS?
intronic splice suppressor
what is the role of ESS?
exonic splice suppressor
what is the role of ISE?
intronic splice enhancer
what is the role of ESE?
exonic splice enhancer
how do SR-family proteins work?
serine/arginine enhance splicing by binding RNA seqs and spliceosome proteins
how do splicing inhibitors work?
bind close to the splice sites prevent spliceosome access
