lecture 8 PT gene regulation idk fuck off Flashcards
What is the conserved sequence found upstream of the polyA site?
AAUAAA, located 10-35 nucleotides upstream of the polyA site.
What is found just downstream of the polyA site?
A G/U or U-rich tract
What is the upstream element required for polyadenylation?
A U-rich upstream element (USE).
Which protein binds the AAUAAA sequence?
Cleavage and polyadenylation specificity factor (CPSF).
Which protein binds the G/U or U-rich tract?
Cleavage stimulatory factor (CstF).
What enzyme is involved in adding the polyA tail?
: PolyA polymerase.
What are the functional roles of the polyA tail?
Enhances RNA export.
Stabilises the 3’ end of the mRNA.
Enhances translation of mRNA.
Acts as a protein-binding element
How long is the polyA tail typically?
Approximately 250 nucleotides.
Are there any exceptions to mRNAs having polyA tails?
Yes, histone mRNAs typically lack a polyA tail.
What is RNA editing?
Nucleotide alterations that result in different or additional nucleotides in the mature RNA.
In which RNA classes does editing occur?
mRNA
tRNA
Ribosomal RNA
What are the two main types of RNA editing?
Insertion/deletion of nucleotides.
Modification (e.g., A→I, C→U, U→C).
What are the medical and biological significances of RNA editing?
Disease: Linked to atherosclerosis.
Brain Function: Implicated in depression and higher brain functions in humans.
Development: Important in Drosophila.
Parasites: Essential for Trypanosoma and Leishmania.
What happens during enzymatic deamination in RNA editing?
Adenosine deamination: Inosine is recognised as guanosine (A→G equivalent).
Cytidine deamination: APOBEC-1 enzyme edits apoB pre-mRNA, linked to cholesterol control and viral replication inhibition.
How does A→I editing affect glutamate receptors?
Decreases Ca²⁺ permeability in channels containing the ‘R’ version.
Editing extent varies across body regions.
Performed by ADAR2.
What is the purpose of mRNA export?
To transport mRNA from the nucleus to the cytoplasm for translation.
Why does mRNA require active transport for export?
Nuclear pores are hydrophobic, whereas RNA is hydrophilic.
Do different classes of RNA follow the same export pathway?
No, pathways vary depending on RNA size and type.
Why is mRNA localisation important?
Ensures localised protein synthesis.
Generates cell polarity (e.g., Bicoid in Drosophila embryos).
Prevents misexpression (e.g., myelin basic protein).
Promotes efficiency in protein targeting.
Enables local control of translation (e.g., synapses).
What are the mechanisms of mRNA localisation?
Diffusion-based: mRNAs diffuse and are trapped by anchor proteins.
Active transport: Recognised by trans-acting factors and transported along the cytoskeleton.
Why is asymmetrical mRNA localisation critical?
Essential for processes requiring localised translation, such as cell polarity and synaptic function.
What additional effects can RNA editing have?
It can add markers to RNA, change protein binding, alter RNA properties, and modify sequences.
Provide examples of mRNA localisation in different organisms.
Ash1 mRNA: Yeast.
Nanos mRNA: Drosophila embryos.
B-actin mRNA: Fibroblasts.
