CMB2001/L08 Post-transcriptional Control II Flashcards
Describe polyadenylation. (2)
Endonuclease cleavage in nascent RNA
Addition of As by polyA polymerase
What is ‘USE’?
U-rich upstream element (5’ end)
Where is the G/U rich tract located?
Just downstream from the polyA site
Where is the conserved AAUAA sequence located?
10-35 nucleotides upstream of the polyA site
Which sequences are bound by proteins required for polyadenylation? (3)
Cleavage and polyadenylation specificity factor (CPSF) binds AAUAA
Cleavage stimulatory factor (CstF) binds G/U
PolyA polymerase
Give 3 functions of the polyA tail.
Enhances export of RNA
Stabilises 3’ end of mRNA
Enhances translation of mRNA
Which mRNAs have a 3’ polyA tail?
All except histones
How long is the polyA tail?
Approx 250 nts
Define RNA editing.
Nucleotide alterations which rsult in different or additional nucleotides in mature RNA
In which 3 major classes of RNA does RNA editing occur?
mRNA
tRNA
Ribosomal RNA (rRNA0
Give the 2 classes of editing.
Insertion/deletion
Modification (A to I, C to U, U to C)
Why is RNA editing in medicine and development significant?
Disease - atherosclerosis
Brain function - human higher brain function and depression
Development - Drosophila
Parasites Trypanosoma Leishmania and Trypanosoma
Mitochondria - potential target for drugs
Name 2 kinds of base modification.
Marked nucleotide (reversible)
Altered identity
Give 2 effects of mRNA editing on start codons.
Creation of start codons by U insertion
Creation of start codons by C to U changes
Give 2 effects of mRNA editing on stop codons.
Creation of stop codons by U insertion
Removal of stop codons by base conversions
Creation of stop codons by C to U changes
Give 2 other effects of mRNA editing on nucleotide sequence.
Creation of new ORFs by nucleotide insertion
Changes in encoded amino acids and splice site choice by base conversion
Describe RNA editing by deamination.
Adenosine converted to inosine by adenosine deaminases
C to U by cytidine deaminases
How is inosine read during translation?
As guanosine
What enzyme carries out cytidine deamination?
APOBEC-1
What is the enzyme APOBEC-1 linked to?
Cholesterol control
Cancer development
Inhibition of viral replication
What level of editing occurs in the intestine and in the liver?
Intestine - editing to produce ApoB-48
Liver - no editing produces ApoB-100
Which long form major component of low density lipoproteins is linked to artherosclerosis?
ApoB-100 including LDL-binding receptor
Which enzyme carries out A to I editing in the Q/r site of glutamate receptors?
ADAR2
How does A to I editing in the Q/R site of glutamate receptors affect Ca2+ permeability?
Decrease in Ca2+ permeability of channels containing ‘R’ version
What is the result of mutations in the mouse ADAR2 gene result in?
Seizures
Post-natal death
Neurodegeneration in hippocampus
Give 3 reasons for mRNA localisation.
Localised protein synthesis
Generate cell polarity
Prevents expression in the wrong place
Promotes efficiency of subsequent protein targeting
Local control of translation
Describe diffusion based localisation.
mRNAs freely diffuse in cytoplasm and are locally entrapped by anchor proteins
Describe active transport based localisation. (2)
mRNA recognised by specific trans-acting factors in the nucleus
Cytoplasmic factors ensure transport along a polarised cytoskeleton
How is mRNA localised asymmetrically in the cytoplasm?
Localised to dendrites or axons enabling synaptic protein synthesis
In embryonic development, specific mRNAs localised to ant/posterior poles of cell to establish polarity and facilitate axis formation
Which mechanisms are used to localise mRNAs?
Active or passive transport
