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23 Cards in this Set

  • Front
  • Back

What is editing?

Modifying the transcript --> localising the transcript.

What is RNA editing?

Nucleotide alterations which result in different or additional nucleotides in the mature RNA.

Which 3 major classes of RNA does editing happen in?




What are the 2 classes of editing?

1) insertion/deletion

2) modification

What is the significance of RNA editing in medicine and development?

Disease - Atherosclerosis

Brain function - higher brain function and depression

Development - Drosophila

Parasites - Trypanosoma

What is editing by base modification?

Can be done by the addition of an extra hydrogen bond (from U --> A)

Can be reversible (doesn't change base pair)

What are some effects of mRNA editing?

Creation of start codons by U insertion.

Creation of start codons by C to U changes.

Creation of new ORF by nucleotide insertion.

Creation of stop codons by U insertion.

Creation of stop codons by C to U changes.

Removal of stop codons by base conversions.

Changes in encoded amino acids and splice site choice by base conversion.

What is N6-methyladenosine?

Most prevalent internal modification in eukaryotic mRNA.

What was the first identified demethylase?

FTO (fat mass and obesity associated protein)

Is associated with obesity (certain alleles)

What are methyltransferases essential in?

Yeast, flies and for embryonic development in arabidopsis, zebra fish.

In mammalian cells they function in stem cell differentiation, circadian rhythm, cell cycle, splicing etc etc.

What does N6-methyladenosine do?

Addition of extra methyl group - does not change base pairing, still pairs with U.

What is RNA editing by deamination?

Enzymatic deamination = A ---> I and C ---> U

Inosine recognised as Guanosine.

Therefore it is the equivalent of an A to G change.

What is an example of RNA editing by deamination?

Cytidine deamination: ApoB mRNA editing.

In the intestine, editing is present and a C --> U change results in a stop codon so the ApoB protein no longer contains an LDL receptor binding site (ApoB-48).

In the liver, editing is not present so the ApoB is translated as normal and forms a protein with the LDL-receptor binding (ApoB-100).

Editing is carried out by APOBEC-1 enzyme.

What is another example of RNA editing by deamination?

A --> I editing in the Q/R site of glutamate receptors.

GluR 2, 5 and 6 are subject to editing (Q --> R). Receptors form tetramers.

Glutamine (Q) is not charged but arginine (R) is positively charged therefore the receptors are directly affected.

What is L-glutatamat and how is it involved in RNA editing by deamination?

It is a major excitatory neurotransmitter.

Editing yields a decrease in Ca2+ permeability of channels containing the 'R' version.

extent of editing varied in different parts of the body.

Editing is carried out by ADAR2 (adenosine deaminase acting on RNA).

What is ribose modification?

2'-O-methylation (happens in cap)

How is stuff exported from the nucleus?

From the nuclear pore.

Small molecules can diffuse through the cell membrane, other stuff has tone actively transported.

How is RNA exported from the nucleus?

Different pathways mediate the export of different classes of RNA.

There is a gradient across the nuclear envelope.

A number of factors are present (Ran GTPase)

What is the role of Ran GTPase?

GTP hydrolysis on Ran.

When Ran is GTP bound, this active form allows export.

For the different classes (tRNA, mRNA, snRNA etc) there are different factors that bind to them.

Why do we need to localise mRNA?

So we get localised protein synthesis.

To generate cell polarity.

Prevents expression in the wrong place.

Promotes efficiency of subsequent protein targeting.

Local control of translation.

Achieved by diverse mechanisms.

Essential fro cell differentiation and function.

(look at examples of each)

What are the 2 ways in which this localisation can happen?

1) Diffusion based-localisation (not in axons)

2) Active transport based-localisation

What is diffusion based-localisation?

How it happens in a small single cell.

Diffusion of mRNA once it's left the nucleus can then lead to entrapment by specific molecules that can bind to it on the cell surface.

This generates a gradient of the mRNA (leads to a local concentration of it).

What is active transport based-localisation?

Achieved by direct transport.

For example, in the cytoskeleton (could be actin based) with motor proteins on it that interact with the RNPs and drive them to functioning --> anchoring.