Lecture 26

Question 1

How is concentration of an mRNA determined?

Answer 1

its rate of synthesis and rate of degradation

Question 2

Mechanism of RNA Degradation (3 types)

Answer 2

Deadenylation-dependent RNA (most common
Deadenylation-independent RNA decay
Endonuclease-mediated RNA decay

Question 3

Shortening of PolyA tail

Answer 3

When <20nt, the PABPC1 is no longer strongly interacting thus decreasing the interaction with 5’ cap and eIF4G

Question 4

Deadenylation-dependent RNA decay

Answer 4

Deadenylase complex removes polyA tail
Two options:
1) 5’ cap is removed by DCP1 and 2 and then XRN1 digests 5’-3’
OR
2) exosome degrades form 3’ to 5’ leaving the cap

Question 5

AUUUA

Answer 5

destabilizes mRNA if found in the 3’ UTR

Question 6

Deadenylation-Independent mRNA decay

Answer 6

DCP 2 and 1 decap the mRNA by association with Edc3 and Rps28B then they are degraded 5’->3’ by XRN1
and eventual deadenylation occurs

Question 7

Endonuclease mediated decay

Answer 7

Endonuclease cleaves the mRNA in two and then 3’->5’ decay occurs by the exosome and the 5’ to 3’ decay is done by XRN1

Question 8

Stability of RNAs (TfR)

Answer 8

In high iron IRE-BP is inactive and the AU rich elements found in IREs are degraded
When low iron IRE-BP becomes active and protects the 3’ UTR and mRNA from degradation

Question 9

microRNAs

Answer 9

Repress translation and induce degradation of specific target mRNAs
556 genes coding for miRNAs
these miRNAs target 60% human mRNAs

Question 10

miRNA targeting mRNAs for degradation

Answer 10

strong base pairs result in endonucleolytic cleavage and weak base pairs lead to deadenylation

Question 11

miRNA synthesis

Answer 11

pri-miRNAs are synthesized by RNA polymers II (has a CTD)
pri-miRNA folds into dsDNA hairpin and drosha recognizes and cleaves it to become a pre-miRNA
Exportin brings it into the cytoplasm
Dicer cleaves ds-pre-miRNA and one of the fragments are loaded onto Argonaute in a RISC complex
ATP hydrolysis unwinds the miRISC and uses miRNA as a guide to target the complementary cellular mRNAs
Binding occurs in 3’ UTR and is unstable by deadenylation

Question 12

Mice with Dicer

Answer 12

No dicer means mice cannot develop embryonically
No dicer in limb don’t develop normal limbs

Question 13

Synthetic miRNAs

Answer 13

Injected or expressed from introduced gene thus making siRNAs -> knockdown

Question 14

Gene Knockdown in MOdel ORganism

Answer 14

POI causes infertility in women affecting 1/100 females in reproductive age
Twins both have variant in MRPL50 it destabilizes mitochondrial ribosome so lower levels of larger ribosomal subunits are observed