RNA Metabolism: RNA Processing Flashcards
Processing of eukaryotic Pre-mRNA
1) 5’ end (capped) 2) internal (splicing introns out) 3) 3’end (polyadenylation)
What is capping?
capping occurs when ser 5 is phosphorylated; nucleotide is added in wrong direction ( connected via 5 prime end with 3’OH on end); 7 methyl guanine (methylation allows for binding to protective proteins); tethered to ctd tail
What is the purpose of capping?
1) protects from exonuclease activity (exonuclease can’t work because of incorrectly placed nucleotide) 2) RNA transport into cytoplasm 3) Translation
3’ Polyadenylation
1) cleavage of RNA 10-30n downstream of 3’ UTR 2) addition of A’s (80-250) to generate a poly A tail
what are the only mRNAs that have poly A tails?
only those who are produced by RNAPII
CPSF
Cleavage/polyadenylation specificity factor (3 subunit protein) recognizes AAUAAA; recruits CtsF (cleavage factors); Recruits PAP (poly A polymerase).
AAUAAA
sequence recognized in RNA 3’ UTR that CPSF binds to.
What are the two different models of termination in eukaryotes?
Torpedo and allosteric termination.
Torpedo Termination
rat1/hxrn2 (exonuclease) tracks along with RNAP,. Pulls RNA out of RNAP. Once it pulls RNA out, RNAP disassociates.
Allosteric Termination
Proteins alter conformation of RNAP causing termination
Why is it more advantageous to have more introns?
1) Diversity 2) regulation via splicing produces different types of mRNAs and subsequently different proteins 3)
Group I/II splicing
Self-splicing; do not require specific factors or ATP; requires two transesterification reactions
Group I
self-splicer; uses guanine nucleoside cofactor; occurs in rRNAs of tetrahymena and mitochondrial regions; 1st cleavage performed by external cofactor guanine
Group II
self-splicer; uses an A residue within intron= forming a branched lariat structure; found in mitochondria and chloroplast pre-mRNAs; 1st cleavage is carried out by 2’OH of A within intron.
Group III
Eukaryotic; spliceosomal introns; the largest class;