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Y2 Genomes > mRNA transport and localisation > Flashcards

mRNA transport and localisation Flashcards

1
Q

What is the nuclear pore complex (NPC) is anchored to?

A

Nuclear lamina

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2
Q

How are proteins and mRNA moved through the nuclear pore complex?

A

Facilitated diffusion

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3
Q

How are proteins selectively transported through the nuclear pore?

A

Nuclear localisation signals (NLS)

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4
Q

What is Ran?

A

Type of Ras GTPase.
Molecular switches are activated by GTPase activating proteins (GAPs) and guanine exchange factors (GEFs)

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5
Q

What is Ran bound to in the cytoplasm and nucleus?

A

Cytoplasm: Ran-GAP
Nucleus: Ran-GEF

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6
Q

What are the carrier proteins through the nuclear pore?

A

Karyopherins:
Importins
Exportins

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7
Q

Outline protein export out of the nucleus

A
  1. Exportin binds to the nuclear export signal (NES) on the protein. These interact with the FG repeat nucleoporins.
  2. Exportin binds tightly to Ran/GTP and moves through the nuclear pore via facilitated diffusion.
    Ran-GAP catalyses hydrolysis to Ran/GDP and the exportin dissociates
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8
Q

Outline protein import into the nucleus

A
  1. Importin binds to the nuclear localisation signal (NLS) on the protein. These interact with the FG repeat nucleoporins.
  2. Importin binds tightly to Ran/GDP and moves through the nuclear pore via facilitated diffusion.
  3. Ran-GEF catalyses conversion to Ran/GTP and the protein dissociates
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9
Q

What karyopherin moves tRNA out of the nucleus?

A

Exportin T

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10
Q

How is mRNA exported from the nucleus?

A

mRNA export is Ran-independent
1. NXF1 binds to RNA , guided by the exon junction complex (EJC). NXF1 also binds and FG repeat nucleoporins
2. RNA helicase Dbp5 disassembles the NXF1/mRNA complex.
3. The EJC remains bound until translation

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11
Q

How can NXF1 depletion be found?

A

FISH

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12
Q

What are the three mechanisms of mRNA localisation?

A

Random diffusion and anchoring
Active transport along microtubules or actin
Selective degradation of mRNA

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13
Q

How is Ash1 mRNA localisedfrom parent to daughter cells?

A

Zip code binding protein She2
Adaptor protein She3
Motor protein Myo4
Actin cables attach the mother and daughter cells

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14
Q

What is the Ash1 gene?

A

Transcriptional repressor which inhibits expression of the HO gene after cell division

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15
Q

How is translation stimulated on mRNA?

A
  1. mRNA caps are bound by (eIF4E/eIF4A/eIF4G) and poly (A) tails are bound by PABP
  2. eIF4G/PABP interactions cause mRNA to circularise, stimulating translation
  3. 4EBPs disrupts the eIF4E/eIF4G interaction, blocking mRNA circularising and therefore translation
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16
Q

What pathway regulates translation in response to nutrient and stress signals?

A

mTOR pathway

17
Q

Outline what mTOR stimulation does

A

Phosphorylates 4EBPs (inactivation) and activating ribosomal protein S6 kinases (S6Ks).
This promotes assemble of the eIF4F complex. This promotes growth

18
Q

How does stress (nutrient deprivation/heat shock) cause translation to globally down-regulate?

A

Stress-activated kinases phosphorylate eIF2α which blocks dissociation of eIF2B, its GEF. This prevents translation initiation

19
Q

How is expression of mammalian ferretin regulated?

A

Iron regulating proteins (IRPs) bind to a 5’ leader, blocking binding of the preinitiation complex to the cap binding complex. This inhibits ferretin translation
They also bind to excess Fe2+, preventing them interacting with the iron response element
Low Fe2+, IRP binds to the stem loop

20
Q

How does Sxl suppress translation?

A

Sxl is an RNA binding protein which contains two RRM domains. This suppresses splice sites and translation.
It blocks the interaction of the preinitiation complex and scans the 5’ leader sequence

21
Q

What is dosage compensation?

A

Equalisation of expression levels within male and female cells with unequal sex chromosome numbers

22
Q

How is dosage compensation acheived?

A

Random inactivation of maternal or paternal x chromosome. The silenced chromosome is visible at the edge of the nucleus and is called the Barr body

23
Q

How does Sxl control msl-2 dosage compensation between males and females?

A

msl-2 transcript encodes male specific lethal 2
In female flies, Sxl blocks splicing of an intron from the msl-2 transcript at the 5’ leader. This retains the splice sites.
In male flies, Sxl is low so the 5’ msl-2 binding sites are spliced out

24
Q

How is the poly (A) tail of mRNA degraded?

A

Exonucleases called deadenylases. The exosome complex is recruited to mRNA to remove the m7G cap. Xrn1 (exonuclease) the does decapping and decay

25
Q

What is translation efficiency inversely proprtional to?

A

mRNA stability:
The more efficient translation, the more unstable mRNA is

26
Q

How can unstable mRNA be differentiated from stable mRNA

A

Unstable mRNA contains AREs which are A/U-rich elements within the 3’ UTR.

27
Q

How is ARE-mediated decay regulated?

A

ARE binding proteins:
AUF1 positively regulates degradation
HuR negatively regulates degradation

28
Q

Outline miRNA RNA turnover

A
  1. miRNAs are processed from primary transcripts by Drosha in the nucleus
  2. This becomes pre-miRNA which is processed by Dicer in the cytoplasm
  3. miRNAs usually anneal to the 3’ UTR of mRNA
  4. RNA induced silencing complexes (RISC) cleave target mRNA, recruit deadenylases and repress translation.
    This accelerates mRNA turnover with irregular base pairing and recruiting deadenylase complexes
29
Q

How can alternative splicing lead to mRNA degredation?

A

mRNAs can be generated with early stop codons. These transcripts are rapidly degraded by nonsense mediated decay.

30
Q

Outline nonsense mediated decay

A

When the termination codon on mRNA is recognised by the ribosome, NMD is triggered if there are not interactions between the ribosome and mRNP.
If there are interactions the termination factor interacts with the poly A binding protein (PABP)

31
Q

How do Sxl promoters used differ between embryonic and adult flies?

A

Early - young females
Late- All males and adult males

32
Q

What binds to acetylated histones?

A

Bromodomains
CRM- chromatin remodeling machine contains a bromodomain

33
Q

What are HATs?

A

Histone Acetyl Transferases

Y2 Genomes (7 decks)

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