lecture 8

Question 1

What is polyadenylation?

Answer 1

Adds an adenine base “tail” to mRNA, which signals the end of mRNA. the “tail” also helps export mRNA from the nucleus, and protects it from breaking down
Conserved 10-35 nucleotides AAUAAA upstream of the polyA site
G/U or U rich tract downstream of polyA site
U rich upstream element “USE”

Question 2

What are the proteins required for polyadenylation?

Answer 2

CPSF (cleavage and polyadenylation specificity factor) - binds AAUAAA
CstF (cleavage stimulatory factor) - binds G/u

Question 3

what is RNA editing?

Answer 3

nucleotide alterations which result in different or additional nucleotides in the mature RNA

Question 4

Which 3 major RNA classes does RNA editing occur in?

Answer 4

mRNA, tRNA, ribosomal RNA

Question 5

What are the two types of RNA editing?

Answer 5

insertion/deletion
modification (changing the coding sequence)

Question 6

Give examples of how RNA editing has improved medicine?

Answer 6

Atherosclerosis
Higher brain function and depression in humans]Tested in Drosophila
Parasites: Trypanosoma, Leishmania, Trypanosoma
Potential target for drugs is mitochondria

Question 7

What are the effects of mRNA editing?

Answer 7

Creation of START codons by U insertion or modification of X->U to produce AUG
Creation of new open reading frames by inserting nucleotides or changing encoded amino acids and splice site choice by base conversion
Creation of STOP codon by U insertion or modification of X->U
Removal of STOP codons by base conversions

Question 8

How does RNA editing by Deamination work?

Answer 8

Converting Adenosine to Inosine
Inosine recognised as Guanosine therefore equivalent to an A->G

Question 9

What is Cytidine Deamination: apoB pre-mRNA editing?

Answer 9

C->U RNA editing carried out by the APOBEC-1 enzymes
Deamination of a C->U in mammalian apoB100 mRNA converts a glutamine codon (CAA) to a termination codon (UAA)
Both edited and non-edited form circulate in blood but with different functions
Longer form is major component of very low density lipoproteins linked to atherosclerosis

Question 10

What is the APOBEC-1 enzyme linked to?

Answer 10

linked to cholesterol control, cancer development and inhibition of viral replication

Question 11

What RNA editing occurs on the Q/R site of Glutamate receptors?

Answer 11

A->I editing on L-glutamate - major excitatory neurotransmitter
Yields decrease in Ca2+ permeability of channels containing the edited version
Editing carried out by ADAR2 (adenosine deaminase acting on RNA)

Question 12

What can RNA editing result in?

Answer 12

Markers being put on RNA
Changes in protein-binding leading to changes in the property of RNA
Change in the sequence
Editing can also occur on ncRNAs and is essential for their function

Question 13

How can asymmetric mRNA be localised

Answer 13

Fluorescence antisense probe binds to mrna part

Question 14

Why localise mRNA?

Answer 14

Localised protein synthesis
Generate cell polarity
Prevents expression in the wrong place
Promotes efficiency of subsequent protein targeting
Local control of translation

Question 15

What is diffusion based localisation?

Answer 15

mRNAs freely diffuse in the cytoplasm and are locally entrapped by anchor proteins
Local entrapment at site where they undergo translation

Question 16

What is active transport based localisation?

Answer 16

mRNA recognised by specific trans-acting factors in the nucleus
Cytoplasmic factors ensure transport along a polarised cytoskeleton