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CHAPTER 38
RNA Processing in Eukaryotes
Problems: 1-5,7,9-11,14
Primary transcripts are processed.
e.g. pre-mRNA is:
• Capped
• Poly adenylated
• Spliced
38:1 Processing of Ribosomal RNA
RNA Pol I
snoRNPs
40S ribosomal 60S ribosomal
subunit
Subunit
(also includes a 5S rRNA
that is made by RNA Pol
III)
38:2 Processing of Transfer RNA
RNA Pol III
• Removal of
intron.
• Cleavage of
5’-leader.
• Removal of
3-trailer.
• Addition of –
CCA at
3’end.
• Base
modification.
38:3 Processing of Messenger RNA
RNA Pol II
Polyadenylation
Capping
Splicing
Capping
• Guanylate base is
methylated at N-7, Step
(3)
2-Hydroxyl groups of last two
riboses may also be
methylated, Step (4)
Increase stability of mRNA.
Enhance mRNA translation.
Polyadenylation
(CPSF = cleavage and
polyadenylation specificity factor)
Increase stability of mRNA; increase half-life.
Enhance mRNA translation.
Splicing of mRNA
Polypyrimidine tract
snRNP
Splicing Mutations → Disease
Alternative Splicing → Protein
Diversity
2n = different mRNAs (proteins)
n = number of alternative splice sites
Transcription and Processing of mRNA are Coupled
CTD (carboxy terminal domain) = YSPTSPS amino acid sequence at the –
COOH terminal of RNA polymerase II.
Phosphorylation of the indicated S
residues leads the CTD to binding of the
factors required for mRNA processing.
The following are all coupled to mRNA
transcription:
1. Capping
2. Splicing
3. Polyadenylation
Post-transcriptional RNA
Editing
38:4 Self-Splicing of Messenger RNA
Ribozymes (group 1 type) are
catalytic RNAs
Lipid transport in
the liver-lipids
synthesized in the
cell.
Stop codon
Group 2 uses the 2’-OH of an A-residue
in the intron instead of a G)
http://ibiomagazine.org/issues/augustissue/discvering-ribozymes.html
Synthesized in intestine
and transport of dietary
lipids chylomicrons.